I owned one many years ago. I think it was Gabbanelli. Those things are probably worth a lot of money in good condition so it looks like you got a heck of a deal! Mine was given to me by a relative who inherited it from a deceased family member. They gave it to me because I was a musician.
I tried to play it for awhile, but yeah it’s too frickin complicated to try to do all those things. I’d say you’ll need lessons from a pro, even to get started with it. Those keys are huge! I don’t remember mine having keys as long as those, more like a standard keyboard. Maybe if you watch enough YouTube videos and practice a lot you might get the hang of it. You’d probably have to break it down and practice one skill at a time until each skill is comfortable, then combine them. Press one key and just work on the bellows, for instance. IIRC, the buttons are for chords, and the keys are for melody.
My memory is dim, but either I advertised or sold the Gabbanelli for $600. I think that’s what I asked, but a husband/wife couple showed up as the only prospective buyers and they wouldn’t pay my asking price (based on some research I did). They probably offered me a few hundred. They both played accordion very well, and were well informed of the value perhaps. Or they were good negotiators.
The Gabbanelli was Italian made IIRC, and very sophisticated looking. I have no idea how that would compare to yours and how that might impact the value.
Maybe this will be helpful:
EDIT: They use accordions a lot in Mexican music, as well as polka of course. If you decide to resell it you might try those types of markets.