Raspberry Pi Pico is a inexpensive dev board for the $1 RP2040 microcontroller that has been used in a *ton* of different projects. It's extremely powerful for its cost and pretty easy to implement into projects. It's also open source, so you'll find a lot of alternative form factors & variations of the Pico that may suit your project better.I know nothing of this Maplepad...nor do I even know what a Pi Pico is XD I assume the pico is some variation of that rasberry pi thingy?
As for Maplepad, I highly recommend giving it a look for your project! Yveltal put a lot of work into it and it's a great idea for embedding into a Dreamcast portable! One thing to keep in mind however is that there seems to be some game compatibility issues, however I'm sure that will eventually be worked out in a future firmware update. (I offered to look into these issues and fix them but I just haven't had the time, with my contest entry and all, lol)
A link to it's Github page can be found here. Hope this helps!