Wood – Hanging a 65″ flat screen tv

If you use decent screws, you should have no problem mounting right to the surface wood, without worrying about where you are behind it. It's a much more robust material than drywall, and 52 lbs is not all that heavy. You could certainly line up the top bracket screws with a strap and use longer screws there, but you probably don't need to.

There's no way to answer this (what will the shelf hold, weight-wise) without knowing what your garage ceiling joists are, if they are part of a truss or just joists, how long the span is, and really, what they were designed to hold up in the first place - many garage ceiling joists are barely in spec to hold drywall, much less a load...

A FAR better attachment method is to place a beam (or more than one) inside the "attic" space across the top of the joists, spanning several, and run threaded rod (steel) through that beam and down through the ceiling to support the item below. In this case it would mean you can spread the load across many more joists (by using a long beam in the attic space.) It also means that you are not depending on wood screws to hold the load directly.