You got it all correct; except you'll have to convert some of your homebrew and roms to be compatible with the supercard. Dont worry though, thats all documented when you buy the supercard, and its really quite simple, it comes with a nice little program for it.
Yes, its just like superpass, and yes its much better. It is a file browser as well.
Also, for all of your gba homebrew needs, and trust me you'll want to run some gba emulators because they are faster than their ds counterparts sometimes, all you need is the supercard. It will also function as a file browser when running gba homebrew.
BTW: Thats the exact setup my friend has, and it all works very well. I think you chose the best "bundle" of devices, for the cheapest price. I have yet to buy my own homebrew stuff, but that will be what i get when i do.
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