So I faced a certain challenge and that is address management in checkout steps, apart from the ability to add an address and edit one. The question comes in two folds :
Should a customer be able to delete an address during the checkout process? and Why? (With references please.)
Should the editing and adding of addresses show as a modal/dialogue form or a form that appears within the page?
As regards being able to delete an address during checkout: I would allow this. This view comes from both personal experience and (so far) a three-to-one survey1 of existing address-management modules in favour of allowing deletion. I can't say why they decide to allow it, but for me, a good reason is that for many people, the only time they'll think about managing addresses is when they flow through the checkout process.
At one time or another I've added various addresses to my Amazon account: sometimes these are more-or-less one-offs (I'm getting something as a gift, and want it delivered straight to the recipient) or as alternate address for my stuff (work address, my parents' address etc.).
Now, I may be unusual, but I rarely think "let's go manage my Amazon address book"... so the only time I'll notice these added addresses, and think "I really don't need XXX's address any more" is when I'm passing through the address-picking step when placing another order. Not being able to delete a no-longer needed address at that point would be annoying.
Something like moving house would be an exception: you would be in full-on "update my address with any organisation I've been in contact with" mode and would probably actively seek out e-commerce sites to update you details. However, for most people moving house is probably a relatively rare event, so "drive-by" deletion (that is, during the checkout process) is, I would argue, a necessary feature.
One argument against allowing deletion of an address is the maxim that the checkout process (and, by extension, the address-selection process) should be as simple and uncluttered as possible. While this is broadly good advice, I don't think it is a good reason not to allow deletion of an address:
Following that maxim is most important for new customers: the less distractions and complications there are (so the theory goes), the more likely you are to convert a prospect into a sale. However, by definition, the question of deleting an address will only apply to existing customers who have already been "converted". That doesn't mean it is "OK" to needlessly complicate a returning customer's screen, but you do not have to be as diligent in removing all strictly unnecessary functions as you would with a new user.
The "extra complication" of a delete option is minimal. There are various ways of arranging an address-book selector (as can be seen by following the references below), but since most already have an Edit button; adding a Delete button should not make much difference.
Although being able to delete during checkout is probably not strictly necessary (most sites will offer an explicit "Manage Address-book" facility), I would argue that the benefit to the user (being able to delete an address when it is in front of them) outweighs the slight extra complication, and saves them having to navigate back into your site after completing the checkout process.
1 Searching the web has (so far) produced the following lists of how different "address modules" (designed to be plugged into e-commerce sites) tackle the ability to delete addresses during the checkout process:
This page about AmeriCommerce's address-book module does offer the ability to delete existing addresses (see, in particular, the screen-shot under What the Customer Sees).
This page about ShopWired's address-book also offers the ability to both edit and delete existing addresses (see first screen-shot).
This page about ID Card Group's address-book offering also allows both editing and deletion of existing addresses (see screen-shot under Adding & Editing in the Address Book).
Based on my personal experience and logic;
1) First time user should have no option to do address management during checkout as it is his first address entered. If the user is returning user and have used more addresses, it is likely that he does not mind adding and chaning addrsses during checkkut, as he is already loyal and this action is not so disruptive or important to change his loyaltiy and opinion.
2) It is more logical to do it inline. You can do it effectivelly with Ajax or some other effects. I havent found clear reference on this, but again logic goes - it is your goal to leave user on similiar interface and not change it too much with pop up (that needs to have contrasted background in order to be visible), especially on sensitive part of the website like checkout.
Difficult to judge without context. During the checkout process, I would definitely allow users to verify (and adjust) their personal information, to make sure everything is up-to-date. However, a standalone option to wipe data may lead to users having to re-enter accidentally removed information.
Modals are highly disruptive and should be avoided when possible. They hide information that is only discoverable by opening the modal. In this case, the modal is likely to take them out of their work flow: simply entering their address.
To address this, let's look at a use case:
I was ordering food using the website Swiggy and have been doing so for the past couple of years. During this time I have moved cities twice. Now in my checkout page, I have multiple addresses I don't use. It is extremely frustrating to not be able to delete my previously saved addresses as I don't have any use for them anymore.
So let me answer your question with another question: Is there any reason why your users shouldn't be able to delete an address?
To answer your second question, it is extremely situational to use or not use a modal. A modal is usually used to remove a user from a process and introduce them to a sub-process. For example, if your address field can take inputs from a map, then opening Google maps to add a marker at their location would be a good candidate for a modal. In your scenario, since adding address is the "main process", I would not recommend using a modal.
User's should be able to add additional addresses, although its most likely to be a use case when a returning customer/user and as a returning user you should be able to select/delete which address card holder/delivery out of the many addresses you say might of gifted items to in the past... Pretty sure ebay and usc are places where I have multiple address and choose the right one for the item. I haven't deleted an address in either of those accounts though... I don't see any harm in giving the user the option edit or delete and add a different address if they change there mind durning the checkout, say if addresses were located in a closed accordion above the next expanded state (card details). They could be go back to address and make the amends.
I'd try to avoid using modals or loading new windows and keep to inline as just good practice but if you have to its full screen overlay in most cases now.
Having the delete address functionality in the checkout process is fine, as long as it is accessible elsewhere. Consider the frequency of checkouts by the user and whether this will add or remove friction each time the user repeats a purchase.
If a user is a frequent shopper at the site, and they are aware that full address management is possible during the checkout process, they are more likely to engage with the shopping-related activities first, even if they are at a different location. Anticipating anxiety should be the top priority, as it is the most significant cause of friction and revenue loss.
Users are anxious if they believe they might lose their shopping cart over navigating elsewhere to update an address. This conflict is magnified on mobile.
Users are anxious if they believe there's a chance they sent the order to the wrong address, deleting it eliminates the error possibility. For example, they had purchased while traveling for work, and know they entered the hotel address, however, there is no incentive to keep this address. As the amount of addresses increases, the possibility of error is more significant.
While avoiding anxiety would also influence the decision of using a form vs. modal, the main concern, in this case, is reducing cognitive load for the user. The cognitive load imposed on a user during checkout is significantly reduced if the context remains the same during the entire process, so I'd advise against the modal. This decision not only helps to achieve the goal (purchase) but it will also free the user from selective attention mode and make them more likely to engage with other aspects of the site, like special promotions, or post-purchase actions.
I don't know what you mean by references. My understanding of this subject comes from studying user behavior and decision making processes, I'd look for research produced on those topics.
