I am planning a bath renovation a few months down the road and I am pretty sure our 30 gallon water heater aint gonna cut it. Its the shower that has me concernced and I'd like some advice as to the size/recovery rates I should be looking at.

The shower will have 3 shower heads with one shower head (approx 2.5) and two Kohler body sprays which give out 2 gpm each. So it looks like 6.5 gpm max. I did a flow test with a 5 gallon bucket in the bathtub and got around 8-9 gpm so it seems like I have enough flow.

This is the only bathroom in the house, so apart from the rare dishwasher/washing machine going at the same time, I just need to compute this for the shower. Can someone help me out?