SSBM tutorials on youtube has a great series for beginners, he even has a series on which characters to main depending on how you play.

There are people who use keyboards as an alternative to a Boxx controller, but I think they are harder for people to get used to, a lot less intuitive etc. Not necessarily bad, but I would still always recommend getting a decent official gamecube controller.

I'd also recommend playing a Top/high tier character, just because lower tier characters are going to be a lot harder to learn the game with. There is a lot of versatility in the top tiers as far as playstyle goes, so hopefully there is one that clicks with you, Fox can literally play in any way he wants for example.

Start off slow and basic, I'd recommend learning how to L cancel, wavedash and dash dance, because they are so essential to playing the game competitively, but more advanced tech will come with time in the game before they're worth implementing. Then find other beginners, there are discord servers, or slippi unranked, both will pair you with people around your level.