A8o in the BB: Figuring out this Commitment Threshold/Planning thing

[private joker]

I'm still working out my bet-sizing, and furthermore I'm clueless as to how we're supposed to change our plan if an ugly card comes off. Flynn/Mehta don't spend much time in the book on what to do if the pot-size shove you were planning to make on the river turns into a bad idea if the wrong card comes off. If they do, I missed it.

Anyway, to the hand: Live 5/10 $400 max, I've got just under 400. Both opponents have me way covered.

3 players limp, the SB folds, and I have red A8o in the BB. I check.

4 to the flop, pot=45.

Flop comes A73 with 2 spades. I lead out for 25, and two players call. At this point, I figured I hadn't yet put in 10% of my stack and I wasn't committed and I was just testing the waters with a 1/2 pot bet to see if my kicker was good. When I'm called in 2 spots I aim to shut down unless I improve, right?

3 to the turn for a pot of 120.

The turn brings the awesome 8c. Now with top 2, I decide I am committed. I have 335 left in my stack, which is ~2 large bets (about 3/4 of the pot) if I am called by one opponent on the turn.

So I bet out 100, right? That's what I did... planning to put the rest in if raised. Now let's say I get one fold and one call. The pot will be 320 and I'll have 235 left. I'm planning to shove the river, of course, but what if it brings a spade? Do I abandon ship and check? Or did I commit myself with the turn bet and should therefore ignore the spade draw and shove absolutely any and all rivers?