If i am going to run a tekin rx8 with a 1900kv motor in it, what C rating should i be looking at getting? Is 25 continuous with a 50 burst enough?

Also for cost effective reasons can i wire 2 2s batteries together to make them 4s batteries?

I'm running a 5000mAh 20C/30C battery on that same setup and it's plenty. I'm sure it depends on your track some. Our track is medium size, but very technical. You don't need a lot of power.

what type of batteries are you using? Im planning to go with turnigys because of the price.

Turnigy. 4S 5000mAh 20C/30C

what type of runtime do u get? Ill be putting this setup in my TEN-T E. Are you running a 1/8 scale buggy?

1/8 buggy. Not sure on total run time, but I can run warm-up laps, and a 5 minute qualifier and the charger only puts about 1800mAh back in. Guessing that is about 6 minutes total, I would say I could get 15-20 minutes anyway.