I am of course very much in agreement with the contributions of my learned friends and much of what I say repeats what they have written. But just to hark back to your final question, Bloo, it all depends on your personal tastes and predilections, I think.
There are some people who only ever want to sit in a session and play with everyone else. Then there are others who are basically not very interested in playing with others and who seem to think of themselves as soloists. The latter often seem to take pride in playing only tunes or settings that practically nobody else does. There is a point at which this becomes competitive, or antisocial, or just boring.
[Edited to add: of course those who are just content to play “session versions” without thinking much about what they are doing can be equally boring.]
Most people though will fall somewhere in between. It’s definitely nice to have a few party pieces up your sleeve in case you get put on the spot at a session, or called up on stage and you want to give a good account of yourself. Then at least people may say, hmm, interesting version you’ve got there, even if they think your playing is pretty ho-hum!
But then, after you’ve been around a bit longer, as Ken said, you might be happy to give a good account of yourself by playing as a solo, I dunno, something that many intermediate players would regard as clichéd and therefore taboo, say The Boys of Bluehill.
You could make a nice job of that tune without doing anything particularly surprising, or you might have made it into “your own version” over the years, with bits and bobs gleaned from other people’s playing of it, other people’s playing of other tunes, or just things that jump out at you out of nowhere as you explore it in a relaxed mood at home - after playing it x000 times over x0 years, something new can often suddenly appear.
(That’s definitely the tack I would take when put on the spot - play something that is well within your abilities, something you can make a nice job of. An ordinary little jig or an ordinary little reel maybe with a few nice touches here and there. Goes over better with those who know than some pretentious new-fangled tune.)
As far as learning variations is concerned, certainly in the early stages of your development it’s a good idea to study and listen to different settings by different players and either consciously work out things they do or sort of unconsciously let what they do rub off on you. All the time bearing in mind that you might want to be able to play a bog-standard version whenever the occasion calls for it.
Having said all that, I wouldn’t worry much about it, Bloo. There’s so much to learn on this path, just learn as much as you can all the time. There’s no particular order to learn things in, no right sequence of steps to reach the goal. And isn’t the easiest way to learn to go for what interests you most?
So I think you should trust your feelings to some extent and take whatever approach suits you. Learn fancy stuff, or learn standard stuff. If you learn it from a good player, you can’t go wrong - no effort will be wasted.