The exterior siding/trim/whatever? 

I'd say exterior landscaping, kitchen, bathroom, windows, doors/garage doors, etc.

Exterior work, new roof Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

For beach properties that are within a few blocks of the beach, how often are you having to repaint the exterior of your house?

Mostly surface cosmetic updates such as new trim, paint, and minor exterior cleaning/fixes.

Currently there is a same sized house with newer exterior paint on my street for 550k, and others that have sold from 540-570k.

I am also looking for how to tackle a cost effective exterior painting.Even I can help the contractor to do the work if that helps, I just don't want to go through the learning curve of the remaining repairs.Thanks I'm advance.

For foundation, go over all the joists and exterior walls - use a flashlight if needed.

They’re also magnets for thieves and vandals.

We have thought of a few different options, going to an interchangeable core system where a "master key" would grant access to exterior and interior doors of all buildings.