If you want to get a little wild and still play on OG hardware, you could play the Gameboy titles on a SNES Super GameBoy or the Gamecube GameBoy Player. I think the Gamecube one is basically a GBA so it would support all the GB titles. But I'm pretty sure the Super GB only supports original GB, not GBC or GBA. Kinda fun to play them on official hardware hooked up to a big screen, although it will probably look not great lol. Otherwise, you really can't do better for GB titles than a GBA sp. As for the DS ones, any 3ds/2ds should work just fine for any of those titles. Although gen 6 and 7 run like shit on an og 3ds/2ds. Not sure about modding or flash carts as I've only used original hardware or occasionally emulation. To answer your question, you can play all of the titles from gen 1-7 between just a GBA and a 3ds. Those are the easiest way to play them on official hardware.
Guitar
I think early on, it's really important to focus on getting comfortable with the instrument itself. When you start learning to play, it's common to have a lot of stiffness in your wrist and fingers. It's kinda foreign for your wrist and hands to move like that at first. Practicing frequently and developing your muscle memory will help get your hands to flow on the instrument.
It's less important when you start, to focus on getting the notes and patterns right. When most people start learning, they sound like shit. It can feel discouraging when you do all this practice and you still don't sound like your favorite band. I think that's where a lot of people end up quitting. And it's why that guy at every party knows how to play Wonderwall and nothing else.
Practice getting a good feel for the instrument. It's a good indication you've become fairly comfortable when you realize you're not looking at your strumming hand anymore as you play. The more comfortable you get, the easier things like the strumming patterns will get too.
Don't be afraid to play something a little differently if it's easier for you to learn. You can use it as a stepping stone to learning the original. Or you can just play your own version.
As far as resources go, I mostly have used YouTube and Ultimate Guitar. I think you'll find that a lot of guitarists don't use sheet music much. The most common form of written music for guitar is written in Tab, so familiarize yourself with that if you aren't already. I have always learned by looking up tabs on a song I wanted to play. You can always look for something else if you are more comfortable with that. But I think it's always easiest to get started on a song with some community-made tabs.
Keep practicing, don't give up. You will get better.
Shantae has a great soundtrack. You also can't go wrong with any of the Gameboy Pokemon titles.
I was unaware of this douche until just now. I've been interested in the Modretro Chromatic for a little while, disappointing to see this guy is tied to it. Glad I haven't gotten one, thanks for letting people know.