First off, welcome to SRK! :3
Now to answer your question, the best way to get into fighting games is to choose a type of fighting game you wish to play. Ultimate Marvel vs Capcom 3 isn’t “hard” to get into but it’s one of those games where there’s a lot going on in the screen at the same time. Id recommend you start off playing a simpler more technical game and understand basic concepts of fighting games that will evolve your talents in other fighting games as well over time. However, there are people who do just fine without having playing previous fighting games. Also understand unlike other genres of gaming, fighting games are going to eat up a lot of your time in the learning curve. Especially in marvel where you don’t understand why you lost… At the beginning. You’ll indefinitely do your fair share of raging but once you learn the core mechanics of marvel, you’ll win games.
Things you will need:
Controller: preferably a arcade stick
I don’t know what your budget is like, but I’d you’re just starting out, I’d recommend starting off a stick instead of learning the cheap pad method. Reason being is because for one, you can play in a arcade setting (If they ever release marvel for arcades lol), two: you can do advanced techniques a lot easier such as plink dashing. If you can’t afford a high end arcade stick, that’s fine. You can start off on a madcatz se or a wwe brawlstick. These sticks can be modded out extremely easily and effortlessly to real arcade quality parts. It will just be a smaller tournament edition fightstick.
Playing on Pad is fine too I that’s your preference but since you come from a pc background, I think sticks will feel right at home for you.
Now everyone has their reasonings behind the systems that they play on. For most people, it’s Xbox. In my experience, it provided a better online service than ps3. You can still find good matches on psn and you won’t have to pay a premium to game. You’d also be preparing yourself for Evo more effectively since ps3 is their system of choice. It’s really up to you and your preferences.