RetroArch doesn’t have Xbox/PS2/switch
No, but EmuDeck does, along with RetroArch… Best have a look before starting.
More power to you if you want to strike out on your own, but you may find it quicker going to join a larger project at this stage, you’ll have people to ask questions to, if you choose well you’ll learn best (or good) practices, etc. Maybe EmuDeck itself? In the end the language doesn’t matter much (maybe avoid Perl, PHP and JavaScript at the start), once you get the concepts down it’s easy to switch to another. You’ve got time, take some to skill up.
And a few people will get extremely rich by siphoning off a percent or two, circle of life baby /s