1) If you mean data files, any file manager - ES File Explorer, Total Commander, etc. If you mean apps, most of them can't be. Of those that can, some can have the entire app moved, but most can have only parts of the app moved. And there's always a link left in internal storage pointing to where the app is in external storage (since the directory entry for the app points to its internal location). You don't save much space by moving apps to the SD card in Android. The idea is to buy a phone with enough internal storage for all the apps you'll need for the nexzt 2 or 3 years (or whatever your phone buying cycle is).
2) You don't unless you either run an app like External 2 Internal (I haven't trried it, so I can't tell you how well it works, but it's free) or a ROM that uses external storage as internal storage (I've used that, back in Android 2.3 days, so I can tell you that, as long as you have a fast SD card [Class 10], that way works fine).
You'll probably find that, in many cases, what you did in iOS can't be done in Android, or it's complicated to do. OTOH, some things you can't do in iOS either come in Android or there are simple apps to do it. (BTW, any friends who iMessage you should send you at least one iMessage specifically marked as text. From then on, any iMessage they send you will be sent as standard text messages. Android phones can't receive iMessages. Apple is "working on the problem". Also, you should have turned iMessage off on your iPhone while it was still in service. If you didn't, all the iMessages being sent to your phone are dieing in the iMessage server. Someone at a Genius Bar can reset that for you didn't do it when you should have.)