A few things you could consider:House Rules: Make sure you have clear, firm house rules for your STR guests regarding noise levels, shared spaces, and respecting the privacy of your LTR tenants.Noise-cancelling measures: You could invest in things like soundproofing the walls or adding landscaping (like thick bushes) along the privacy fence to further dampen any noise between units.Separate Access: If possible, ensure that the STR and LTR tenants have separate entrances or parking areas.

I've told him no multiple times, that I'm firm on the agreed upon price since he had time ample time for due diligence and if he wants lower, then I want to void the cancel the sales agreement so that I can put it back on market. 

Yes, this is in Florida.This property is located in a desirable area in Florida.

These ordinances make clear the state does not desire any jurisdiction from removing safe unpermitted units. 

Even in the “gentrified” neighborhoods of Federal Hill, Fells Point, Canton, Harbor East, desirability can be very block by block so you have to be careful that you understand these neighborhoods (and blocks within) somewhat intimately.

That's where they fly in, that's where the jobs are, stay as central as possible and your home will be desirable as a rental of any kind, and for resale value.

Our firm has found great value in that.

If you're looking for an accountant / book keeper reach out and I have an excellent referral for a firm that is virtual, does only real estate investing, and their accounting work is incredible. 

Ty so much for such a thoughtful and knowledgeable answer. we are pretty close on the purchase deal terms and will start marketing our group of 10+1 duplexes just as soon as we have a firm deal.

When working with Civil Engineering, Is it best to simple pick on firm and go with them, Or is the 3 quote rule in effect at this stage of the process?