Flow is an issue. A larger ( 3/4") water supply all the way from the WH would be recommended. Proper selection of valves is important, and multiple heads usually dictate a loop design on the pipes to equalize pressure. Any good plumbing store, or mfg website, can provide details of this. If you plan long showers at multiples of 2.5 gpm (one head) think about a larger WH.