Should I show these sidebar tabs all at once or when requested?

Question

On my web application, when my users click on an action that requires me to show a form, I do it by sliding out a sidebar with the form within it. The action buttons are spread out on differents part of the application, they are only stacked together for demo purposes in the picture.

Anyway, I'm trying to create a way for users to being able to work with several of these forms at once. So I'm going to implement tabs for the sidebar and I have two ways to go about this. Not sure which one is best:

Option 1 - Showing a new tab whenever a user clicks on an action button

1. User clicks on an action button
2. Slidebar comes out with one tab
3. User clicks on another action button
4. One tab is added to the sidebar and focus is put on it

Option 2 - Showing all tabs at once

1. User clicks on an action button
2. Slidebar comes out with all possible tabs visible

Answer 1

I suggest you should go with something akin to multiple palette windows (like gmail does for chat and compose email) that could be maximized or minimized as needed. This would allow for the user to exploit the maximum space available in the sidebar and act on multiple forms simultaneously as required.

You could present the forms in the sidebar as below:

Also, since the maximize, minimize and close icons are already familiar to the user due to their universal understanding, there would be no confusion as to what the particular icons would do.