Jay,
For an electric motor to run the same speed forward and reverse it's timing has to be '0' (no advance/retardation). There can still be a slight difference between those speeds but usually not all that much. If you could catagorize motors as 'racing' and 'normal', then the 'normal' motors should work just fine.
A bow thruster will usually require one channel, depending on how it's set up. For -independent- control figure one channel. Bow thrusters can also be wired so that they turn on with full throw of the rudder. In that case, no seperate channel is required.
Almost all ESCs allow proportional throttle control no matter what it's ratings for amount of power (100%F - 50%R). The percentages apply to the amount of current supplied to the motor in that particular direction. [The 'almost' in the first sentence is a 'hedge' cuz I'm not familiar with all ESCs. There's bound to be one that doesn't allow proportional throttle control, I just haven't seen it.]
At my age I don't have 'blonde' moments. It's called 'C.R.S.' syndrome, and is usually expected of 'old farts'. Makes for a good excuse anyway...
- 'Doc