welcome to the forums whacker!

yes, a brushless tail motor can be used with a 3n1/g90. i use something similar myself, but with gears instead of DD. since the equipment is pretty much the same, i recommend using the geared 5300kV long can setup for better performance. it's a little heavier than other tails, but the power and response time do more than make up for the weight.

if you use hh with a stock brushed main motor, a gws DD would be more economical and provide all the performance you'll need for now ($12 vs $75); the power of a brushless tail isn't really worth it until you have a brushless main to go with it.

i'm sure nobody told you heli's would be cheap.