Hey, welcome to the forums.
A great start would be to try using @guu’s fantastic auto expanding image based on the latest version of the OS. (0.4)
(Some people prefer using older versions for compatibility/performance reasons)
If you haven’t already got one, find a program that you can use on your computer to “SSH” into your device. Lots of people use FileZilla here it seems. I personally use Cyberduck. It’s all just personal preference. Alternatively, you can use a command line interface, like Terminal, or Putty. If you’re learning, seeing things graphically is much more familiar. Just be careful not to drag files or folders into the wrong place, as this can mess things up!
@Rebusmind made a post listing some alternative standalone emulators if you’re not satisfied with the speed of the included ones. Each of them should be a link to their respective github pages, that should contain installation instructions.
The only other thing you will then need to do is source some BIOS files for some emulators, and put them in the correct location. If an emulator doesn’t work, it is most likely needing a BIOS. Try using the search to find the emulator name + BIOS to find the solution to your problems.
This OS version actually comes with a lot of emulators. As for ROMS, that’s something that you’ll need to work out yourself. Selling a pre made 128GB card for money, filled with ROMS is an extremely Grey area, and is … let’s just say, frowned upon.
There would be a lot of expectations when it comes to having a pre made card, and would no doubt result in a lot of back and forth communication to get things working.
Doing it yourself, you really understand how it works, and can troubleshoot it much better. Plus you have a great community to help you, right here. Why not ask around here for help setting up emulators?
There are a few other troubleshooting issues that some people need to deal with. I’ve tried to answer as many of them as I can when I see them. Click on my profile, and go through my activity to see what I’ve answered if you want. Or if you see another user who mainly answers questions, chances are you can see them answering another question you may have, or pointing out a feature that you didn’t know of.