4 brief questions (I just cut the game at move 74). Feel free to answer!

I'm not sure what value can be put on my advice, since I am much weaker than you, but to me a move somewhere around tengen looks good. It would give you a sort of moyo in the middle/right, looks at making use of the aji left in those two dead stones at G10, and strengthens your not-yet-quite-safe group in the bottom left.

Where did you play?

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Poka King of the south east.

Likewise, I'm weaker than you so not sure if my opinion means much, but my instinct was to make the move you made in the "a or b" situations. I'd probably like black to take black, though white's positions all look so carefree maybe I'm just getting greedy thinking about black's big moyos. I'd want to play d18 as black, but I guess since you're both 4d and left that area alone, it's probably not severe, and something helping black's group in the lower left would be better.

The game looks fairly close to me, maybe a little better for B. Without the G9 mistake, I would say B for sure, but that was a big loss. Anyway, it looks like B can now block at O14 and prevent W from breaking through, thus making a big moyo. I would play there.

O14 was my first instinct too, but I was worried about white O6 in response. How should black deal with it? If black defends the right side, a move around J6 next looks severe.