I'm not the best when I comes to gearing. I tried a similar spur/pinion that you have when I first got my NEU. It just didn't do it justice. I do not think it will hurt it to run it that way. The NEU is a great motor and well I expected more from it then the 66/22 I was running on it. Once I did the mod to the tranny and got some Jato spurs it was more to what I expected. I didn't know what to expect really. I now know that the efficiency of the motor is important. Not just how fast it went. Here's a link to a thread in the brushless forum about the tranny mod. It is really easy to do and not real expensive. You will be needing some 5mm pinions unless you already have some. It is a good mod to do. Not sure what you are running for your slipper but the revo spec holds up real well. Not like the stock e-maxx with the slipper pegs. THat worked okay for a stock setup but you'll be needed a better slipper setup with the upgrade you have planned. I was told to get a pinion and use the spurs to make adjustments. I run a Jato spur 54t and use a 26t pinion. It fits what I like to do. Tell it's just nice not being limited to the novak gear ratio. FREEDOM.
http://www.rc-monster.com/forum/showthread.php?t=6232
As far as lipo batteries. There are a lot of them out there, but I would get the best you could afford. If you skimp to save money it comes back to bite you later. I found that out. I haven't bought any in a while. I've read that most of guys are getting them in the 25c-30c. Hopefully someone will jump in give you some better advice on which ones to look into. I bought mine over 6months ago. I have like (6) 2s 6000mah and they do me fine. Nice thing about this forum that If I give some bad advice. Someone will read it and set it right. I don't think this is bad advice but not onto of the lipos. So I would say for a min on the discharge of 25c (maybe 20c) and no lower then 6000mah.