(As always, take with a grain of salt... I'm quite weak myself.)

First, you've probably been told this already, but it's better to play human opponents than AI opponents. You're more likely to pick up weird habits from imitating the AI (which does smart things which are impossible to copy, and dumb things which are easy to copy), and equally weird habits from exploiting its weaknesses, and besides, when you play humans you can adjust your handicap to your strength more easily.

16: My instinct is that both H3 and P2 are bigger. If you play P2 and white moves elsewhere, this move becomes very big. H3 solidifies the profit you got from attacking the white stones.

18: This move is so-so for the same reason that the kick is frequently so-so... it lets W make an ideal extension. I think if you pincer here, white has few good options. I suspect the kick is better, though, because it normally forces F4 and then gives you breathing room to take C6.

24: This is okay, but don't think of it as an invasion. Think of it as a placement; you're putting stones inside white's group to ruin his eye space. Notice that you have miai of J1 and G1 to connect these stones out.

28: Yes, you normally don't ignore a contact play.

30: Too late. Not sure what this accomplishes at this point.

32: Not bad. You should note that, since W has ignored your play, a move at G2 becomes very big.

34: No, this is good. Frequently in this situation B would invade at 3-3; comparatively, this invasion is good.

42: This is double bad. First, F17 is really, really dead, so you don't want to play another stone so close to it; that's throwing good money after bad. Second, you normally play around B14 or C14 here, to get more of the corner. Without that extra move, B is dead. Third, W will often reply to a move around C14, so you may have lost sente for nothing.

44: Neither of your options is ideal. Do some tewari analysis. If W plays Q2 on move 7, where do you reply? If W plays Q2 on move 43, where do you reply?