Can a ½ inch water pipe supply enough pressure for a shower head and body sprayers?
For copper pipe, hot (~50 C) water should only flow at approx 5 ft/second. Flow of less than one or two ft/sec can also be a problem. Based on the diameter of the pipe (1/2 in type L), 0.72 gpm flows at 1.0 ft/second, so this would suggest a maximum of 3.6 gpm for the pipe (assuming 5 ft/second). Also, you must worry about the pressure drop. Use table 6 of The copper Handbook, at 5 gpm, the pressure loss is 0.161 psi/ft. Assuming your supply is 50 psi, and you need 35 psi to be delivered to the shower head, you can have a maximum pipe length of (50-35)/.161=93 ft. Figure 7 shows how fittings should be counted due to their larger pressure drop. A 90 degree fitting counts as one foot. Additionally, water pressure will decrease with elevation by approximately 0.433 psi/foot.

As long as you meet these two restrictions, you're fine. Since you need 4.5 gpm, and your pipe is likely less than 93 feet, things should work fine.