Ask your friend about that.
We just get whatever we think is good or whatever.
Low end for me is Kraken which I don't think you'd really want...
Mid end would probably be the China clones and whatnot
High end would be something like TM, SystemA, etc.
May I ask where you'd be playing? Is it mostly CQB and indoor fields or outdoor fields? That should be taken into account when picking a gun (or variant).
I'd say be prepared to spend at least $450 off the bat for a used gun off the classifieds.
First thing, protective gear, ballistic goggles or PB mask, gloves (for the thorny bushes), kneepads (your knees will thank you for this),
Second thing you should do is get some good footwear, go to marks work wearhouse or an outdoors shop to test out a few boots to pick the right ones. I have a bit of a bias for getting good footwear though. IMHO You'll be spending most of the day on your feet and they move you around so get your self whatever keeps your feet comfortable. I got my boots from an outdoors shop and I use them for hiking, yardwork, etc. I even have Superfeet insoles (you don't *need* them but I muse say they are awesome).
After that, get your primary (MP5), mags, battery, charger etc.
Get your BDU's and something to hold your mags in (a chestrig or vest but chestrig is what most of us use).
The last thing you should be picking up is your secondary (in your case your glock). That is unless you'll be competing in CAPS.
NOTE: You CAN show up to games in a sweatshirt, t-shirt and jeans/cargo pants and either use a hi-cap or mid cap and keep the mags in your pocket or something. Wear white so people know you're a noob