There are some times when hiring a Pro makes sense. IMO, this is one of them.
If you're just doing the tub, that's fine. However, I have my 'reservations' about doing the walls. I haven't sought out an explanation on this as to how they do the tiled walls. I hope they don't just glaze over the tiles w/the grout still in place! With that, the wall would look like a solid mess. At the same time, I'm guessing the glaze will wear off the grout at random times causing the wall to look like #$%*@. And lastly, I HOPE that when I find out that I'm told to remove the grout first for the reglazing, THEN re-grout. That way, it will look like a TILED wall.