"From an installation perspective, will it be difficult to install one 60 inch vanity?"

No.

There will be no difference in durability between a veneered door and a solid door.

since the final location is close to 60" i think i'd worry if any part of the trip from the doorway straight back to the wall is less than 60". like around door or window casings...baseboards...the path from the door up a staircase, etc. in general i'd take joseph's word for it but i'm a worrier.

The really hard part is cutting a filler to only 1/4”. It would be easier on an amateur to use a partial overlay cabinet instead of a full overlay one. Then scribe molding could easily cover the gap as it can mount in the faceframe.

HI -- Usually bathroom and kitchen cabinets come in sections .

This is off topic, but how many kids do you have? If three, make the 3 drawers equal size. If two or four, do 4 shorter drawers and give each child 1 or 2. For fairness.

If you have more than four, give them shower caddies to move their prized shower gel and fancy schmancy razors back and forth between their bedrooms, make the middle section open for storing rolled towels, etc. For peacefulness :-)

OP, Joseph is always right so that answers that.

Question for Lindsay, sorry to hijack, But I have three kids and I think your shower caddy idea is genius. So are you saying each kid keeps their own personal toiletries in their own personal caddy in their bedrooms, and then takes it to the shower with them, college-style? That way no one complains that so-and-so used my fancy shampoo or clogged up my razor?

Genius. Totally stealing that one!!

That's exactly it! I only have two teenagers thus far but it has relieved so much tension, especially for daughter #1.

Feel free to "steal" it all you like :)

That hasn't been a problem so far @Colette :-)

We went to a local store that sells Starmark cabinetry and does bathroom renovation projects. We were told that since we are going from partial overlay to full overlay doors, we would need to reduce the cabinet width so that the door does not bang into the cabinet. The designer at the store said that we should order a 58'' side cabinet and have two 1 1/8'' fillers (for the sides). I think that we are going to go with one cabinet (modified down to 58'') since three cabinets would cost more.

We have two kids sharing one bathroom. Our counter top is a mess with all of their stuff. I need to figure out how to organize their items better.

" I need to figure out how to organize their items better."

Three cabinets would cost more, but how much is a tidy countertop, organized drawers, and peaceful siblings worth to you? The cost difference might well be a worthwhile investment in the peace of your home.

Two kitchen designers said that since I am converting from a partial overlay door to a full overlay door, I need to add more space between the wall and the cabinet (so that the door does not bang into the wall). My wall to wall opening is 60 1/2''. They said that my total cabinet width can not be more than 58''. I will have spacer/fillers on both sides of the cabinet.

remember you wont lose any countertop because of this... you'll still get the full width, over the filler.

i'd try for a configuration that gives a centered sink, with equal storage on each side, but that of course is up to you.

And if you do a bank of drawers on each side, there is no door to bang the wall and you can go the full width.

Drawers will maximize your storage and organization ability in a way cupboards never can.