1. How will you access those valves once the shower and tub are complete.
2. You cannot use braided supplies inside the wall. Someday they WILL fail and cause a flood.
3. If the way to connect the two devices is not self evident to you, perhaps a plumber might be the better way to go. DIY may be an ego booster, but tearing out a shower because something does not work or is broken can be demeaning.