It also depends on if your developers work native of hybrid.
If native is the case, you can design screens that use all of the OS's features for every OS. If you work hybrid you need one solution for all.
If hybrid is the case...,
...make sure that your main functions and navigation works for all operating systems.
In other words, users should be able to go to all screens and perform every action regardless of OS. Long press actions should be something you think about, but do not make a certain action exclusive to this. For example, you can delete an item from a list by touching the delete icon, but also by a menu that pops up after a long press on iOS. Do not make this action exclusive to the long press. Not even all iPhones have long press actions.
Android has a back button. They call it the 'up button'. See here.
The Up button returns users to the previous screen they viewed. It
navigates upward in the app’s hierarchy until the app’s home screen is
My concern would be more about the navigation bar in the bottom half of the Android screen. iOS does not have that. How do you use that space on different systems?