You are correct in that we can't say you're losing or breakeven but since there are probably less than 10 players in the entire world who have a winrate of 3BB/100 or better at the stakes they are currently playing, and yes that includes micros aside from the very smallest stakes, over what would be considered a significant sample size (i.e. 200k hands+) and these guys are the best players at their stakes assuming that you can match that winrate right out of the gate is also presumptuous and assuming you're going to keep winning at 4.5BB/100 that'd probably put you in a class of 1 so, yes you probably are running hot atm, that doesn't mean you're not a winning player. We're not saying you're not a winning player, what we're saying is that atm you probably are running hot in terms of winrate and probably are just on a high.
Yes it's very possible you have a decent edge in the game because you just don't play crappy hands but I'm afraid the times where someone played a tight preflop game and played a fit/fold postflop game and took home 3BB/100+ are long gone at anything above 0.25/0.50, and even at 0.25/0.50 I'd say it'll be tough to maintain.
It's great you've started off as well as you have and it's also, as Sherlock Holmes says, is as much of a departure from the truth to underestimate yourself as exaggerate your qualities but you do have to be aware of just how big of a role variance plays, I'd say over a 10k hand stretch the vast majority of your winrate is decided through variance, yes your skill edge will have something to do with it but given the short period the sheer range of what your winrate can be over that period, even if you're a winning player is too big
Yes you can "feel" you have an edge but there's no way to determine how big it is unless you are up against completely godawful players.
And to answer some of your questions:
1) Yes I cold call 3 from the BB and fold on the flop. I'm getting 7-2 to play my hand preflop so I can play a lot of hands and on certain boards it's safe to fold and I shouldn't be fishing vs obviously strong ranges with much of my range. 3/5 is just a sample size issue, they could have called with JTs, QTs etc and the flop come AA5r, not really much you can do there
2) Calling river with 3rd pair is fine and in fact if you're against an aggressive player folding it is godawful

