G'day kinetic, I think you will find the badger patriot is double action brush, don't bother with a single action unless you are decorating cakes(with vodka)!
As for siphon or gravity it really depends on what you want to do, for fine art and illustration then a gravity or side feed,but there is nowt wrong with having them all in your arsenal!.
To begin with its really all about finding the pitfalls and getting the paint reductions, air pressure and control correct, get them nailed and your off.
It can be a steep learning curve but an enjoyable one, and if you get decent kit from the off the you know the problems you will encounter will be you and not the brush
Happy AB'ing mate and we are all here to advise.