It's my understanding that extra check valves with a well system aren't a good idea. Now, it's not a bad idea to have a vacuum breaker on a WH (and may be required some places). The requirement to raise a WH, I think, only applies to gas-fired ones and the newest ones no longer require it functinally, but code may not have been adjusted yet. Brass can be connected to copper without any problems. In some places, the flexible copper supply lines are required (earthquake country), so with a quality line would be fine (not all are created equal). The T&P valve must be piped down within (I think) 6" of the floor. Some situations require it to go to a drain, don't know about yours.