First thing you should do is head over to YouTube so you can find out what your phone is capable of and how to do it.
If there is anything you don't like about the phone (software), head over to the Andoird Marketplace, since you can fix pretty much anything you don't like (i.e. keyboard). I've kept the default keyboard as it uses Swype, which makes typing long messages very quick'n'easy.
for music, yes just connect via USB to the Computer, and drag'n'drop. There is no set folder - you can choose where and how to store/organise your music, and Android will search for it and add it to your library. There are apps to mark fodlers as 'not containing media' so that they don't get scanned. There are also other music players (i.e. PowerAmp is good). If You've got Wifi at home, definately give Samsung KiesAir a go - makes downloading/uploading stuff from/to your phone very easy. I use it for grabbing photos, etc.
Also, if you've got Ebay you might want to get one of these: Premium Micro USB Host Mode OTG Cable for Samsung Galaxy S2/SII i9100 | eBay
It allows you to connect your USB stick to your phone to read/write files from there. I use it to copy movies to my phone. You can also use it to connect a keyboard and mouse, I think. There's plenty more you can do, but you can find that on YouTube or just browse the app store (plety of free stuff there - I've not spent a cent in the marketplace yet) :)