Where could I have done better in all of these games? Any feedback would be helpful. Thanks!
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In the first game, you are losing an exchange in the final position because of 23...Ba3 (eg, 24. Ra1 Bb2). The question is whether your impending capture of the pawn on b6 provides sufficient counterplay. I think that it doesn't.
Earlier in the game, you shouldn't have done all of those exchanges in the centre (you correctly suspected that you were wrong to do this). The reason is that you are giving up your developed pieces and allowing Black to improve the placement of his pieces without loss of time. For example, 11. dxc5 Bxc5 simply develops a Black bishop. If you wanted to exchange on c5, you should have waited for Black to move the f8 bishop first.
There's a rule that grandmasters follow. It goes like this: "To take is a mistake". Your eleventh move is an example of this.
I hope these tips help you to improve your game.
Jane
In the third game, you ask a question about opening theory at move 14. I find that the website 365chess.com is a good place to check out opening moves. It seems that the most common move is 14.fxg3, but Black scores very well from this position. One strong-ish White player did achieve a draw with 14.f3 Qb6 15. Nd5.