Whatever gun you choose to buy, research into it first as much as you can. Try to go to a walkon and ask someone if you can have a go.
Most guns, when setup properly, will shoot the same. My mini will do the same job as an SL8R, except on the SL8R you can mess around with a billion settings, and see it all on a fancy screen and text your mates in game (Im making this up) but it will still shoot someone in the face, like any gun these days. So don't worry about looks or gadgets or what-have-you, especially if you are on a budget, just go for performance.
Barrel choice. Personally I would buy one barrel. Get yourself a .693 bore size barrel. Honestly, a barrel is a barrel is a barrel. Just get one, with decent porting (like a 3rd of the way down the barrel) and you'll be good to go.
Hopper, depends, a Halo/Reloader is a great choice, but you could get an Empire Revvy or an Egg and it would be perfect aswell.
If you have any questions (i.e what the hell is a Revvy Bolter?) then please just ask