I think Cas covered things nicely. Being the gun guy is a fairly uncomplicated role that can let you learn the rules of the game. The other three get a little more complicated. It doesn't take a whole lot of build points to get really good at shooting - max agility, max firearms skill group, heavy weapons, qualities to help out the specific kind of shooter you want to be; Ambidextrous for dual wielding pistols, for example. In your case, add Armorer as well.
Do not, by any means, go with the pre-gen weapon specialist in the book. As a combat person, you want at least 3 Initiative passes, you can pick them up pretty easily and cheaply with Wired Reflexes 2. Once you have your combat basics covered, be sure and pick up at least a couple other useful skills.
Anyway, whatever you pick, have a blast with it =) and feel free to ask if you want advice or anything - I love making example characters =)