Hello 
1) Trying to figure out sizings in big pots can often be frustrating if we don't dedicate some time to thinking about it both at and away from the table. The worst thing is firing a bet in a large pot & realizing that the stack sizes are really awkward on the next street. It's awkward when stacks don't fit neatly into a 1-street or 2-street plan.. you aren't sure whether you're committed or not, etc. So we want to avoid those situations by making things as simple & effective as possible.
When we're in a big pot we naturally want to think about the effective stacks & how to fit the stack sizes into a 2-street or 3-street plan. This is quite easy to do heads-up but a bit more complicated if there's more than one player in the pot & their stack size changes things. I don't have a lot of experience in multi-way squeezed pots, but in general it's good to know that in 3-bet pots it's perfectly OK to use smaller sizings than you would normally use in a single-raised pot.
For example, if we imagined that we knew CO would be folding 100% of the time to a c-bet on the flop & we would be heads-up against the BU, the eff. stacks are around 128bb on the flop. We could create a 2-street or a 3-street plan in this situation. If we wanted to play our stack for 2 streets it would involve betting about 30bb into 38bb which leaves us with a pot-sized shove for the turn. However, say we're holding a bluff which we're planning to check/fold on the turn if our flop bet gets called - we would still be betting 30bb here, just as we would be if we were planning to shove the turn. Ideally our checking range on the turn will also contain most (or all) of our non-vulnerable value hands especially vs aggressive players, & then our shoving range will also contain some bluffs with good equity as well as our vulnerable value shoves.
As you can see in this example we are not pot committed on the turn
In your own hand you've suggested that you are pot committed on the turn when you really aren't at all.
If we want to create a 3-street plan, it's clear we'd need to bet a lot smaller on all streets. If we bet about 16bb into 38bb on the flop & 28bb into 70bb on the turn, we'd still have a good 84bb into 126bb shove on the river. Even in this example we are not committed to the pot after we double barrel, & we can resort to a similar strategy which we used for the 2-street plan, except now we are much less inclined to check some value hands. Some bluffs can be check/folded, some bluffs can be shoved, previous value bets could be check/called or check/folded, value hands can be shoved, etc. In general if the board is drawy & your opponent has some of those draws in his range, you want to be creating a 2-street plan if possible, whereas if the board is dry it is usually preferable to stick to a 3-street plan.
Some basic guidelines for thinking about sizing & I hope it helps you 
2) I think we have what's almost close to a value bet on the flop, & knowing that there are large chunks of their range which we want to protect our hand against & extract value from, a bet on the flop is probably a good idea.
Board: 7♦6♦7♣
Equity Win Tie
CO 24.07% 23.40% 0.67% { JJ-77, QdQh, QdQs, QhQs, AQs, 98s, 87s, KdQd, AdJd, KdJd, QdJd, AdTd, JdTd, Td9d, AQo+ }
BU 27.84% 27.66% 0.18% { TT-44, ATs, A7s-A6s, KJs, QJs, J9s+, 97s+, 87s, 76s, KdTd, QdTd, Ad9d, Kd9d, Qd9d, Td9d, Ad8d, Td8d, Ad5d, Ad4d, Ad3d, AhTd, AsTd, AsTh, AcTd, AcTh, AcTs }
SB 48.09% 47.60% 0.49% { JhJc }
However, it's probably likely that we're going to need to check at some point in the hand, so checking the flop might not be a terrible idea. I don't think I would personally do it though!
Hope this has helped! ♠_biggrin: