First off, Welcome
Intro
I know the temptation is great but if you're intending to actually play airsoft rather than plink in the garden we always advise playing the three games so you can be UKARA registered and then buy a Realistic Imitation Firearm (RIF) not a painted one. You will no doubt want to upgrade your gun to something better or change type in future but painted guns (IFs) are hard to sell and you will loose quite a lot of your investment. Talk to the site you played before and see if they'll count the previous games towards the 3 to get UKARA
BB spitting machine
I don't know how set you are on that particular model but I would say you can get something cheaper for the same performance. Look at CYMA and SpecnaArms range.
Or spend a bit more for a metal body and a few other improvements. Personally I think the SpecnaArms EDGE range are very good for the money but again, buying a painted one would be a poor investment.
Magazines
Any M4 mag
should fit. (more investigation may be required once you have the gun)
You have to decide if you want Mid or High capacity...
Mid-Caps = around 120BBs
+ Bit more realistic with more mag changes required.
+ Silent when running etc.
- More mags needed so more expense and carrying capacity required.
Hi-Caps = around 400BBs
+ More firepower without mag change
+ Fewer mags need to be carried
- Less realistic with regular winding needed
- Lots of noise when running etc.
Battery (Look for 7.4v LiPo, higher mAh better)
Check for specific gun battery space
THIS If you get a gun with a T-connector (DEANS) or
THIS If you get a gun with MiniTamiya connector
THIS is a bit more pricey but same power and smaller so more likely to fit. (Look at gun info for connector type. Will be either Mini-Tamiya or DEANS)
Note: DEANS is the better connector
Charger (Get the best you can afford to keep batteries in good health for years)
1)
THIS as minimum
2)
THIS is better but only has MiniTamiya connector so for DEANS you'll need
THIS
3)
THIS is the one I use. It charges any kind of battery with monitoring. (UK one is out of stock so get this if you can change the plug or get a UK cable)
If using MiniTamiya then you will also need
THIS
(Others will hopefully have suggestions)
BBs
No real preference for starting out.
0.25g-0.28g are a good general weight for most but 0.2g are OK to start.