Hi, and welcome.
1) Yes, but SD is much easier than USB - USB either needs an externally powered drive or a USB flash stick which draws very little power. It's a little hit or miss. Make sure you get one which is confirmed to work if you go the USB route. But as I say, SD is 100% reliable.
2) You can use it for anything once jailbroken. Only for pics and vids if you are stock.
3) You need an app like iFile (from the Cydia store once you are jailbroken). This is a bit like Windows explorer / OSX Finder and lets you have full access to the iPad's storage and connected devices.
4) No, you can't install apps on an external drive. IOS isn't built that way. Sorry. Should have bought a 64GB!
Hope that helps. One last thing though. There is no guarantee that you will get a 4.3.3 iPad2 which is the ONLY one you can jailbreak, and the chances are diminishing every day. There is no way round downgrading a new one that you get if it does not have this version. You will be stuck with a stock device until a JB is released for IOS5 (it is very unlikely there will be anything else for 4.x now).