Preflop play is OK but I'd probably prefer to limp (there are already two previous limpers, which give you awesome pot odds)
I don't like betting 20 in-position on the flop because you are basically giving your out-of-position opponents a chance to attack back (someone slow-playing trips that was giving you a free-card for example). When we make this types of bets we should ask ourselves "what's the point of this move?". There are four main reasons why we want to bet in poker, in order of importance:
- Value betting: we expect to have a stronger hand and want out opponents to call to win a bigger pot. Doesnt' seem the case here.
- Bluffing: We have a weak hand but we think our opponent will fold enough of his medium-strength hands to make our bet profitable. If we bet on this spot, this is what we should aim for. And a bet of just 20 doesn't seem to acomplish anything. Oddly enough, it actually did work and one of your oppoents folded!!
- Hand protection: Our hand is not strong enough to value-bet but we'd rather see our opponent folding than giving him a free card. This only really makes sesne when the villain's range is basically a big pile of trash.
- Information: we bet to narrow down the opponent's range (a range is just the set of hands our opponents could have in a given spot)
In conclusion, there are two approaches to this flop. Either make a larget bet (50% of pot should be enough because you were the preflop aggressor adn this plot doesn't seem to have helped any of your opponents. This is kind of a weird hand because in this case it did!). This is definitely what I would do if I were against a single villain. The other option is to check and get a free card (ideal if you were against, say, 5 opponents)
In the turn we definitely want to bet and we want our opponent to call. There will be enough time to fear full-houses and slow the action down if things go out of hand. Since we don't really know much about what our opponent could be holding (some strong hands and straight draws, but mostly a lot of trash), a 50% pot could be okay (had we made a 50% bet in the flop we could go larger because we could get more value from his range)
In the river, unless his all-in was something like 10 times the pot, we hold one of the strongest hands we could have here so we do have to call (we still beat many 9x hands and it could be a bluff on a missed straight draw)