My son was definitely a tummy sleeper as a baby and it was either "do what we are 'supposed to' and get lousy sleep" or "let him sleep happy and WE get to sleep too" As long as he could raise his head and turn it from side to side and the room wasn't too warm, there were no fluffy blankets/etc in his crib, we didn't smoke, no pets, etc etc (read up on possible SIDS causes and remove all you can) then dont worry! Also the risk for SIDS decreases after 2 months I think (my boy is 6 1/2 years old now)
I actually think that allowing him to sleep on his tummy once he is able to lift and turn his head does him a service. If he doesnt have any issues while napping, then I think you can let him sleep during the night on his tummy.
WHY are you afraid to let him sleep on his tummy? Because of how he is, or because "they" say you're supposed to put baby on his back to sleep? If this is the only reason, phooey, you/he are fine. If you truly see things to be concerned about while he is napping on his tummy, then follow your gut feeling until you see he can handle it.
My baby didnt have acid reflux but still spit up (burp cloths are standard baby gear). I dont know how much is normal and how much indicates a problem though. I'd probably not feed him right before bed and then lay him down (My husband is one of those who can't eat before bedtime or he gets acid reflux. Me, I dont like to go to bed on an empty tummy. Oh well.) Let your son's meal have time to settle down in his tummy before laying down, sleeping, etc.
Enjoy!! Don't worry overly much about every warning and such. ENJOY these moments and celebrate that you son will sleep well on his tummy. And get some sleep yourself!