I don't have one yet (I have a hold on a BRB, waiting for warmer weather to ship). I have been doing research for a while. The humidity thing is pretty easy to solve with daily misting and an enclosure that is not glass. Even glass can work but it's a little more work. I have an Animal Plastics PVC cage waiting for my future girl.
Babies can be nippy, some are some aren't. They grow out of it. Adults are easy to handle when adults by yourself. Males tend to get 5-6 feet while females can reach 8, but they are slender compare to red tails.
For food, I'm pretty sure rats are the biggest ever needed. Most start out on mice then work up to rats. If they are anything like my BCI boa, they will take food without question.
If you are not comfortable with the humidity needs of a baby, try to get a yearling or adult. They don't need humidity quote as high. Provide a large water bowl and a humid hide and you would be set.
Also don't let the temps get too high, they don't tolerate too much heat. Even though they are considered an Intermediate snake, they still are not that difficult to take care of. A pet rat or hamster needs much more attention than a rainbow boa.