I recently moved into Android development myself. I've got many years of development experience, but decided to wade into the shallow end of Android development.
Which means I was pretty much doing similar things to what you have been doing, but my perspective differs because of experience.
Having said that, I originally started out with the "one screen == one activity" approach, and quickly learned its limitations.
Which works after a fashion. Invariably, I will use some sort of finite state machine, and so activities became the states... simple enough, I thought.
Then I came to the realization that whenever I press the back button, I go to whatever the previous activity is.
This may or may not be a big deal to your game, but consider the following:
You are in the OverworldActivity(using familiar Final Fantasy-esque terminology), wandering around the world, when suddenly you have an encounter and go to the CombatActivity.
If, at this point, you hit the back button, your game goes back to the overworld.
And that is unacceptable to me, and I'm almost certain unacceptable to you.
Yes, you could put handlers into the Activities so that if you are at an invalid activity it sends you to the correct one, but really the better thing to do is to design activities with the "can I safely hit the back button and still have the game play make sense".
So, here's a scheme that is more likely to work for an FF style game:
- MainMenuActivity(has the "start/resume", "instructions", "about")
- HelpActivity (self explanatory)
- AboutActivity (also self explanatory)
- GamePlayActivity(does the world wandering, combat, and most other game aspects that cannot fit into the "go back" scheme, hitting the back button goes back to the MainMenuActivity, which makes sense)
- InventoryActivity(you get here from the GamePlayActivity, and so it makes sense that you "go back" to the GamePlayActivity
- ShopActivity (when you enter a shop/inn/whatever)
- DialogActivity (presuming you can end a conversation at any time by hitting the back button)
And hopefully this helps.