Should I fill 3/4-inch gaps along the wall before laying ceramic tile?
I wouldn't bother for two reasons. One, it's unlikely that there will ever be any load placed on the tile close enough to the wall to cause breakage. Two, you may be installing baseboard trim or base shoe, which will cover most of that gap anyway. 

If you have reasons to disagree, fill the gap with mortar as you tile. Consider laying a row of fiberglass tape along the wall to help prevent cracking.