I was advised once - by the UK CAA - that turning the prop backwards has absolutely no effect on the possibility of engine start - it can still fire up if all else is in place (just as easily as turning it forwards).
The second point they made was about the vac pumps - but, as said, was a bigger drama to the dry type.
The third point was that if - like most - you turn the prop by cupping your hand around the leading edge to rotate backwards or trailing edge to rotate forwards....what will happen if it does start.
Rotating forward - the prop will move away from your cupped hand (may still rap your knucles with the next blade if you don't move quick enough). Rotating backwards - by cupping the leading edge - the engine will fire into your hand (and that will hurt!!).
All three reasons said "if you need to turn the prop - do it forwards".