Actually the Neu 1512.1d is being used by quite a few of the buggy guys, you really cant go wrong with Neu..
3s is ok, 4s is ideal (personnel opinion) you’ll be able to hang with the Nitro brothers and get 30+ runtimes with the right mAH lipo.. You should / need to measure the clearance you have once the battery holder is installed to the bottom of you body; again most Buggy guys are running 4s. I'm going to be running 5s on mine but I’ll probably need to shim the body 1 to 2mm for it to fit.
Just spend some quality time in the buggy threads reviewing other team members posts, feel free to ask any and all questions, you’ll find that 99.9 percent of the guys on there are extremely knowledgeable and are absolutely willing to discuss their builds with you..
hope that helps??
have a great one
P.S.
Here review this link of the teams thoguhts for a 4s. It's by Drift Buggy..
http://www.rc-monster.com/forum/showthread.php?t=12268