Eveal is quite physically fit. Actually, physically, I'd think he's able to compete in boxing or any other sport.
Technique wise however;
Eveal, seeing from your videos, I'd say you will need a lot of time to prepare for amateur boxing. Your boxing style, is more or less professional styled as in you hit to hurt. In amateur boxing, you just need to hit, it doesn't matter if it hurts or not, you just need to hit, even if it's a sloppy technique which couldn't knock out a fly, it will score.
Kickboxing. Seeing as you have a lot of background in boxing, going into kickboxing won't be much of a pain to be honest. Just need to learn how to do a few kicks, concentrate on leg kicks and checking with the front thrust, and then depending on the type of kickboxing style maybe work the clinch a bit. When it comes to competition, I'd highly advice you to work using your fists because you're really an ace with them. Stay inside, and if they persist on being on the outside, kick their legs and move in. As for punching vs kicking, if they kick, move in and batter them with your punches.
MMA; Go to the nearest grappling gym, work how to do takedowns and a few basic locks. But most importantly, seeing how you're a predominantly a striker, learn how to shift from position to position where you could strike from. Look at Crocop, he learnt only how to hold his own in grappling, no submission whatsoever, only how to sprawl, move from positions to positions, escape and then he just ground 'n pounds his way to victory if people take him down.
Other than that:- I can't think anymore. I'll update as things pop into my head.
I got two fists.. Don't make me use my head as well!