A 60” piece of furniture without a waterproof top does NOT fit in a 61” space. It would need to be a 68” space, minimum. 72” would be even better. You need 4” minimum clear space on either side gor cleaning and other maintenance. At 1/2”, you can’t even fit a pinky at the sides to swipe out cobwebs. Much less a paint brush. Plus, sinks at 43”H are virtually unusable. Water would run down your arms and onto the not suitably waterproofed vanity and onto the floor. The new standard height for vanity sink tops is 36” tall. Thats what an undermount ee sink and 36”H vanity gives you.

You really need to put a full stop to this and hire a designer. Design isn’t about pretty colors and nice stone. Design is making sure the math works so you don’t expend effort on something completely unusable.

Put that piece in a foyer or dining room, where it belongs.carry a tape measure with you wherever you go. Learn ergonomics and building codes and design standards. Or take the easy route and just hire the designer who already knows all of that.

That is a pretty buffet. I agree that it will end up too tall, unless your family and friends are all 6ft+ tall.

24-inch mirrors should work, but that also has to take in consideration of, how they fit in the wall space, In that case, 18" vanity lights would work. You could cut the legs down on that piece to make it a bit lower, however, I fear you will lose a lot of storage space to plumbing.

What you really need to do is tape it all out on the wall. that will help you.

https://www.tradewindsimports.com/blog/standard-height-bathroom-vanity/

Vessel sinks do not get installed on 37" high vanities. I don't think your buffet will fit in the allotted space.