Go to http://bowjackson.com/ and they have a bunch of different calculators to figure KE, FOC, Arrow trajectory, ETC...

You do not need to shoot 300 fps to hunt inside of 40 yards. 250+ will be plenty fast. Your Bowtech will certainly produce enough speed and KE to hunt anything that you want to. To decide on a head weight the only real good way is to buy field tips in different weights and just shoot to see which one flys better. You may need to do some minor tweeking of the bow when switching different weights. Usually on an average hunting weight arrow the 100 and 125 grain heads fly the best.

One more thing to think about is that the faster the arrow the more fletching control you may need when using fixed broadheads. Longer vanes or more helical or offset of the vanes.