The toilet needs 15" OC to either side, so you're okay with that. The height of the tub spout must be above the lip of the tub, dropping a few more inches might let it splash, but may not, and it isn't a code issue. It's rare that the trap will line up unless you have exactly the same tub...you'll probably need to rework that a bit. If they used tubular verses glue-up fittings, it may fit after you loosen things up. There should be a vapor barrier behind the cbu, and it should lap over the tiling flange. You can notch the studs that 1/4" if you want.