I'd say stick with the stock barrel. If you are just starting off you will never notice the difference between the stock barrel and any of the aftermarket barrels. If you are shooting uspsa you won't need it as we aren't shooting at any x rings. I'll mimic post #3 in that I wouldn't spend a lot of money on a trigger right now, get a spring and connector kit. A magwell does help but you can shoot limited without it for sure if you want to cut costs. The only thing I would really suggest is a new set up sights, TTI are what I use and they are great. You can also pick up a few TTI basepads for limted.
On a side note, if you are going to be shooting limited I would suggest your choice be in .40 (22 or 35) as you will be scored minor with 9mm