That's my problem: we don't have a lot in the way of palms and bananas up here, so I would probably have to improvise, and hope I neither starve the plants, nor burn them up with a chem imbalance.

Good quality compost and lots of it, 10-10-10 is fine too they are not picky

I would use a much higher number. Every 2 or 3 weeks

For example: I have a double mahoi in a 22" pot, just getting started, ~3' tall. If I give it 1 cup of composted cow manure+some bone meal every other week until it's 5' tall, then same each week after that while the weather in CT is 'hot', would that be about right?

At the moment, nights are down to low 40's, so growth is still slow.

Bananas won't do anything is nights are in the low 40's and fertilizing won't help unless it is warm/hot. I would suggest a high nitrogen fertilizer