You might post this question on johnbridge.com
I'm not a tile pro, but I did tile a shower and here's what I believe:
1. That price is reasonable for the labor, assuming yr tiling only 3 walls and no ceiling, and assuming there's no design, inlay or niche work. 3 days seems quick. I'd figure 2 days to tile, 1 to grout, 1 to seal. Only go with a 'tiler' not a 'handyman who tiles'. The devil's in the details. You want an artist - not someone who just wants to get through it fast. There's no verifying the price of the materials; you can spend $250 or $5000 or anywhere in between for a shower that size.
2. I wouldn't butt the joints. Use a 1/16" joint if you don't want to clean much. Also, use Spectralock grout. It's an epoxy grout that won't stain. It's about 5-10x the price of regular cement, grout though. You might use spectralock on the floor and nonsanded on the wall. If you do that though, make sure the colors match.
3. I'd use ceramic. It's easier to install and easier to clean. Stone is porous, so it needs to be sealed more frequently or it'll stain. Glazed ceramic won't require sealing. It's also lighter and thinner than stone, so you won't need a special thinset. If you use natural stone, the bullnoses are harder to come by, so it might jack the price up - especially if he has to grind his own.
4. Speaking of thinset, if your tiler wants to use mastic instead of thinset, it'll tell you that he doesn't do this often. NEVER use mastic in a wet location.