How tall are your ceilings, how high do you want your mirror hung. These issues play into a sense of proportion too.

What do have BELOW the counter? Does it float? That proportion is just as important as what you are contemplating

I'd suggest you do an ELEVATION on paper, of what you are planning, floor to ceiling and wall to wall at 1" to one foot scale, include mirror and lighting: )

Sometimes you get what you need not want. I find that thickness for the counte might work but what is your vanity height , style etc. We need pics and for sure some clue as to the size of the space and pics of the vanity IMHO the inspo pic is a confused design the trim on backsplash is very traditional and that very thick counter very modern so which style is yours?

Make sure your fabricator knows how to do basic miters properly, never mind bigger ones. We have seen a few awful miters on the kitchen forums recently.

When we built, my kitchen designer did elevation of all the cabinets. I used those scaled drawings to figure out the exact placement of everything in the space. I wasn't leaving any of the design decisions to the GC or trades!