Hi,
I personaly haven't got one of those flash kids but I can answer a couple of your questions
.
1. Yes if you download the rom (exact copy of the gba game) then you have the game like you would buy it in the shops. Roms are the same as image file sort ta speak for cd-roms
2. Don't know
3. Yes they realy work on the gba. Some roms might need patches but they can be found on gamecopyworld section console.
4. The kit consist out of two things. One flash card and one loader. If I may be so boled has to advice you one to get it would be this one (####://www.divineo.co.uk/cgi-bin/div-uk/uk-gba-fl256) this kit consist out of a 256mb flash card (biggest ever) and one Loader which you need to copy the game to the flashcard.
Hope this helps you out a bid. I myself was wating for a 256mb flash card which is now out so I am going to get me one soon.