I'd like to know if there are any tricks to stacking one cake tier on top of another without (a)ruining the frosting on the bottom tier while setting the top one on and (b) actually holding a cake while trying to put it on top of another one. It is so hard to hold a cake just by the cardboard without dropping it, and then taking your fingers out when you actually set it on top of another cake. Any suggestions/advice/hints would be so appreciated. Thanks!

You can try a large spatula (or pizza lifter) - slide it under the cake, lift it up, and then place on the lower tier. That way, no fingers are involved.

You can also cut your support dowels to the right size, but then raise them up out of the lower tier about 1/2 an inch to an inch. Set the top tier on the dowels - the space allows room for your fingers not to touch anything - and then the weight of the top tier will sink the dowels back down into place.

I personally use a combination of these methods and have had good luck with that.

Sure. Use SPS! You can sliiiiide your top tier in place without ever touching the icing.