It's a crappy designed a/c system which can't cool the house sufficiently?

I believe this varies by city/state, but in California, designating a prepaid "last month rent" means that it can only be used for that purpose (even if the rent goes up during tenancy) while the security deposit may be used for repairs, damage and for any unpaid rents.

I am in the process of finishing construction plans on a really cool industrial design loft multiplex.

If you do need an owner rep my first suggestion would be to approach the architect who did the design and see what their fees are for doing this.

Yes consult the entire design team, architect, structural, civil.

Because I'm an engineer, my first step is to draw up plans (do a design). 

@Nicholas Gessner actually that happens to be one of my listings, zoning is area specific, LH (limited historic) where you are looking is designated ground level can be retail/office, upstairs can be residential.

@Deborah Asbury the best way to find contractors is to talk to architects, designers, engineers, realtors, investors as well as other contractors that are too busy.

If you haven't come across AirDNA (www.airdna.co) yet, I'd recommend checking it out - seems like a very well-designed tool for evaluating STR markets.

“[Homebuyers] are attracted to the development mainly due to the site’s attributes and architectural design of the building,” says Eugene Lim, key executive officer of ERA Realty Network.Located in District 3, One Pearl Bank is within walking distance of Chinatown and is the only development atop Pearl’s Hill.