The recommended distance from the centerline of the toilet to anything else is 18", but the minimum required is 15", which is tight but doable.

I'm a little unclear on how long the shower space is and where the shower head is going, but here's an idea. Put the shower head on the same wall as the toilet plumbing and leave an opening in the long shower glass wall right before it gets to the corner at the foot of the shower. Don't put a door in it. If your shower is replacing a 60" tub, that should be plenty of length so that you don't splash water out the door opening. My sister has a shower like that and I love it - why have a door if it isn't actually necessary? You could put a pony wall right there as you enter the bathroom with glass above, same for the long wall. Or you could do glass for the whole thing. I'd do at least the short side pony wall, but that's me.

Unfortunately, the shower head cannot go on the toilet wall as it's an exterior wall - I'm in Canada. Also, the ceiling is only 6' tall there, and my husband is 6'2"! ugh. So our plan was to put the rainhead on the long interior wall, so that it points down off a 15" arm.

The current tub is only 50" long and then there's the 6" wide pony wall.

Well, that changes things. I'd still put the door on the long side furthest from the toilet. A simple door is probably best. A sliding door probably means a track and tracks tend to collect yuk. I'd put the hinge on the toilet side, but either would do.

My in-laws put in a sink like the one you're looking at into their very tiny only bathroom maybe 5'0" x 9'8". It looked good. The problem is you need other surfaces to set things on like soap, hairbrush, toothbrush. I like hiding the plumbing. This is an adobe house and there were some issues with the 1940's plumbing, so we had to make some repairs in the tub/shower (adobe walls on two sides covered in concrete) and took the opportunity to refresh the bathroom. One of the things we did was to replace the good looking sink with a more functional small vanity. The three kids who live there were so excited! They also liked the new medicine cabinet, the light that was actually bright, and the turquoise bottom half of the room. Small things.

Thanks for your help, suzanne_sl. :)

Luckily my husband and I are minimalist so don't need tons of storage; room for a vanity seems like such a luxury! haha We keep a lot of stuff in the master and will have a Kohler inset medicine cabinet, too.

Oh, and I found a pretty perfect picture from Style at Home showcasing what I think you're suggesting: