If the unit is vacant, how can they guarantee a price based on the rent unless you delay the closing until the lease is signed?  

I would imagine that how/when they pass along rents is stipulated clearly in the management agreement you signed with them.

After all is said and done, signed off on and closed, can I create an in-law that collects rent and not have it considered a 5 family (town is fine with it so that's not the question) But as we know  a 5th "apartment' pushes me into commercial in ways I'm not interested in,  so only want a 4 fam with a legal in-law if possible.  

Although this may be the case and it can cause frustration, I'm determined to not let it sway my purchase criteria.

super exciting, congrats...watch out for remaining open and pulling permits..Duval, border counties, like never before are targeting dumpsters, we buy houses signs, dinging for anything, door permits, etc....I "think" its because of insurance companies, and past hurricanes, the county is hunting and penalizing hard like never before......aggressively  against investors..the city turns a blind eye to children not in school during the day, rather than enforcing, but is looking for rehab investors to penalize and enforce.....maybe thats where the $$ is..

The Seller's got a contract signed with a foundation repair company with a guarantied quote, then wrote us a check for the amount needed.

I stand by my statement, and based on the few details provided here, it's more than just likely this space would not be a fit for a national restaurant tenant (either as franchisee or corporate signed deal). $1 psf/mo NNN ($12 psf/yr) NNN speaks volumes about the location from a national restaurant chain perspective. 

Do I fill out what I know already before I sit down and sign with seller?

Buyer in the beginning did not want to be represented, buyer declined services from listing agency, LA accepted offer with buyers agent on the contract along with signed agency disclosure.

On 9/14 I signed closing docs, expecting to receive funds the following business day.