Raspberry Pi - I assume emulation is possible but not sure how to do it; please help

[Kilyle]

Note: Please move this to a more appropriate section. I'm not all that familiar with this place and apparently chose poorly; my apologies.

So my nephew and I are looking at getting a Raspberry Pi. He's 9 and not yet a programmer; I'm 34 and a hobbyist programmer. We've both used lots of emulation before (I love retro games) and I'm looking forward to the possibility of getting the Pi to run little ROM collections... and maybe even get a hex editor and start hacking 'em - and teaching my nephew to hack as well.

As I understand the Raspberry Pi: $30 computer, minimalist operating system called Raspbian (free software Linux thing), I'll have to get the hardware separately (monitor, keyboard, trackball), and we'll get a USB hub for plugging in multiple things. And you swap out entire operating systems by switching SD cards, so it's kind of like going back to the days when you had to use floppy disks to boot up.

I've never used Linux; I grew up using DOS and am used to Windows. So I've got some questions about how this will all work out. Especially, I want a head's-up about any compatibility issues I might not be aware of, and any extra things I'm going to have to mess with to get it all working. So these questions are for anyone who knows the Raspberry Pi, and/or anyone who knows Linux (particularly Debian):

Software-wise:

I assume it's possible to load up an SD card with an operating system, an emulator or three, and a bunch of ROMs. Is this difficult? The files themselves are tiny (at least, ROMs are tiny and I think emulators aren't huge... actually, I'm expecting Linux emulators to be smaller than Windows ones), so I don't anticipate any problems putting a bunch on one SD card. I assume at some point we'll have a small library of SD cards, including one with my nephew's favorite ROMs (and everything necessary to run them), another with mine, and a third with educational games, etc. I'd say each ROM card would also have Minecraft, but I'm not sure how much space the world save files will take, so Minecraft might need its own cards.

Secondly, the ability to hack ROMs. I assume I'll be able to stick a hex editor and maybe one of those ROM graphics viewers on there too. Suggestions for specific software choices? I have a little experience with hacking but not a lot; mostly I've messed with the text different characters say, or the names of items etc. I'm going to be careful because, as I understand it, it's possible to make the kind of mistake that has a ROM go outside its boundaries and start messing up files or even the operating system itself, but I figure this would be easy to recover by just re-ghosting (hope I'm using that term correctly) the SD card. Since ideally the hacking stuff would be on a separate SD card (rather than on the same card as our regular playable ROM collections), there won't be any lost save files.

And lastly, I assume I'll be putting programs etc. on the SD card using my Windows computer, then giving the cards to the Pi, rather than using the Pi to download and install programs directly, even though it has ethernet. Any wrong thinking here?

Hardware-wise:

I assume it's possible to hook up one or more controllers (NES, SNES, or Genesis) through the USB hub. I've never hooked up controllers to my computer (except for one guitar controller); is there anything special about the Raspberry Pi that would make this difficult or troublesome?

I... guess that's it with the questions. Anything else you can advise me with regards to the Raspberry Pi? Thanks for the help!