Anyway, we have one house that will be vacant within the next few months and it will most likely be a gut rehab (3 bed, 1 bath, 912 sq ft).

They would gut a deer and dump the guts right into a garbage can.

I completely gutted both units and updated them.

Bathroom and kitchen are gutted so I can't really have an appraiser walk through and get an accurate valuation.

A good contractor can give you an estimated cost of the major jobs like updating wiring, gutting a bathroom, updating kitchen cabinets, cost per sq.ft on carpet vs LVP, etc.

Do an analysis with those close to you and go with your gut.

Regarding initial rehab, someone who does a full rehab (full gut, all new appliances, fixtures, outlets etc) should theoretically encounter a lot less maintenance/repair expenses for the first 5-10 years...

Each unit has separate utilities and electric.2 units with tenants get all new appliances, new kitchen cabinets/granite counters, new light fixtures and a 'light' bathroom update (resurface tubs, update vanity and light). 2 units that were vacated were completely gutted and redone, including the above mentioned and new shower/tub inserts and plumbing. 

The property is gutted to the studs and I would like to insure it throughout the renovation process.

You only have issue if total loss fire or if you do a full gut rehab moving around walls but even then you can usually rebuild same number of units as was on doc its just going to have to be up to the new codes.