It is entirely up to you, of course, but you may want to read this:
Use different screens wisely
- Before starting to create another screen, first you should think about is it really necessary?
- See also Building apps with many screens and SteveJG's post about advantages/disadvantages, because in only one screen you also can use vertical arrangements to simulate different screens, just set the arrangements to visible = true/false as needed...
- See also Martyn_HK's example about how to use Tabs in App Inventor and another example from Cyd. and my Tabbed Screens Demo
If you decided to use different screens, then you should switch them correctly, else you will run out of memory after a while...
The recommended method of switching screens in App Inventor
(Thanks Taifun)
Also see demo: multiscreen.aia
and