[onewhippedpuppy]

What JD said. If you can get underneath the front edge to pry up a bit on the top, you're golden. If it doesn't easily pry up, use a sawzall to cut off the nails/screws. If it's an older house, 95% chance they are nails. It may also be easier to cut the top in half to remove, sometimes it's hard to remove tops like that when they are in between walls, at least without damaging the walls/stuff on walls.

I agree on the tub, you're probably SOL. I've installed a similar set-up, and it required access from the underside. Personally, I'd prefer to patch sheetrock than mess with tile, so I would cut a hole in the wall.

The other work looks very good, should be a very nice bath when you're done. Me, I get to refinish the walls of a half bath after stripping wallpaper, then lay underlayment and tile. I also get to tear off a tiled countertop, new Onyx top comes in next week. I also need to stock up on beer.