I do everything myself, so for what its worth, here are my comments:
TILE - Don't lay tile over tile. If this is over a concrete slab, you have a perfect tile base, so use it. After old tile is taken up, if the previous tile was laid with (eek!) adhesive from a bucket instead of mortar, the old adhesive needs to be scraped/ground off. Then after cleaning floor with just water, let it dry. Specify that Red Gard be used over the concrete slab before tiling. It is a roll-on decoupling membrane, and will reduce the chances of any cracking with foundation movement. It goes on fast, and takes overnight to cure. Directions must be followed to get a thick enough film. If the tiling is not going to occur soon after, then cardboard should be laid over it to keep the Red Gard layer clean and undamaged.
Use only
Porcelain tile. Porcelain tile is a vastly superior product for many reasons. And is not that all much more than the garden variety "ceramic tile", which is just a glaze layer over crappy base tile clay.
Don't tile around anything. Pull the vanity, so the vanity will go back over the new floor tile.
Use thin-set mortar, Flexbond is a good one. Do NOT use an adhesive! Adhesive is popular, because: It's cheaper, it's faster, it requires less skill, and its crappy. Water infusion over time can loosen adhesive, and then you've got a real $ mess to try to fix. All those historic sites in the old world where fancy tile has lasted for thousands of years did NOT use adhesive!
Do not (and I see this all over!) grout up to a wall, tub, etc. Use matching color silicone caulk there instead. This avoids the inevitable cracking that will occur due to movement between surfaces. Done properly, the color-matched silicone will look just like the grout. The same problem exists in shower stalls between wall and floor, and wall to wall.
Heated Tile - If this is over a concrete slab, don't waste the $$$. It will not work well. The concrete slab is a giant thermal sink, and will be difficult to heat to any reasonable/worthwhile temp rise in a reasonable time. Sure, you could have a wall timer that automatically starts the floor heater cables up 6 hrs. before you may use the shower, but why?
Toilet - To each his own. The human body was not designed to sit at "chair height" for #2. It was a squat. In many parts of the world, you will find the Porcelain tray... I think the whole "chair height" is a gimmick to sell more fixtures and installation services. If in a wheelchair, I can see its advantages. We all ain't in wheelchairs, that's for sure. Maybe some are just so out of shape (read "too big") to handle a bit of flexing for a regular height toilet. Like I said up top, to each his own. I won't install them. Only regular.
Remember that a contractor will be there only for the job - he or she will not be living with the work year after year like you will. A lot of corner-cutting goes on to make the job quicker and cheaper, and competitive with others who look for a low price.
Well, I've probably done enough damage here, so I'll go away now
