Sounds great. Shorty packs will go in the Serpent fine, transverse as standard or inline if you cut down some of the chassis. Capacity doesn't matter with LiPos as it did with NiMh or NiCads, you're only going to be using about 1500mah at the most during a 5 minute race. Two packs is more than adequate for a day of racing. The C rating is what is important - the higher the value, the more "punch" the cells have. 100C is hard to beat, even with the quality of today's cells.
Charger-wise, as long as you can balance charge LiPos, there's no need to buy anything expensive. I bought a £50 Overlander RC-6S AC Pro charger in 2012 and it's never missed a beat. Any similar models (the HPI Reactor 500 looks to be identical, or very closely related) will be more than adequate - the SkyRC RS16 you mentioned looks fine. You can run from a 12v outdoors, if you're running indoors you should be able to find a wall socket. When you do come round to charging LiPos, there are countless guides online as to how to properly do it. As long as you're not daft with them you'll have no issues.
Car-wise, you won't be disappointed with the Serpent. The only thing we run differently from standard on the team is the RudeBits acetal idler gears, other than that it's absolutely bulletproof. I've had several hefty whacks (both indoors and outdoors) that would've taken wishbones clean off on my old Schumacher, and the MM has come out without a scratch. You'll find it incredibly easy to drive, not twitchy, and a breeze to set up - we have setup sheets over on
www.serpentuk.com if you ever get stuck. The Facebook group Serpent Spyder is also a great place for help and general advice.
