My biggest recommendation to you is take a class in Longarming to decide if you even LIKE longarming. An Intro course that involves loading the top, batting and backing on the rack and doing different things, like panto, FMQ, and templates.
Most dealers offer this sort of thing as well as shops who have longarms available for rental.
Then go to the big shows and try out as MANY as you can. Set a budget. A rack set up can run from as little as $6K to as much as $36K.
Obviously the less computer and arm space you have the less it will cost. Consider your reach. I have a 26" and can barely utilize all that space because I don't have the reach. A 22" would have been fine. I have a stitch regulator and have no desire to have a computer driven LA.
Most people who start this journey do their research and homework for a year or more before finally settling on a make and model.