Here's my guide for buying a first gun that i wish i used.
Find a model, G36 m4 Mp5 Ak47 doesn't matter. Just make sure its an AEG.
if you're on a budget, look at brands like CYMA, JG, DBOYS or other clone companies. With the money you have left, pay a gun doc to re grease, shimm, and put in the spring you want. If you play outdoors, m110 (370 fps), if indoors, m100 (340 fps). I have to use an m90 (290 fps) for my CQB field. With the money you have left, ask your gundoc for internal recommendations and do it. Gundocs are pretty knowlegable about that kinda stuff.
As for the batteries, one up for the hobbyking. A 7.4 will not wreck your gun. Any gun is 7.4 lipo ready. You'll need a lipo charger. If you buy a cheap one, make sure you watch it when it charges.