I find that two of the biggest mistakes are in the manner in which you ask for the money (there is a good way and a not so good way) and not having enough knowledge on the subject and the proper info on the presentation of the deal itself.When I need to fund I deal, I am not asking for money, I am offering a legitimate and alternative opportunity for others to make money.

Although the majority of Michael's superb content on Cost Seg focuses on how to properly assess the value of Cost Seg, he also does highlight some items regarding the internal workings of a Cost Seg study.

With regard to the contractor, you want to give proper notice for when the contractor will come to do work and that depends on your state's laws and also your lease.If you give proper notice and the tenant refuses entry, then I would talk to the tenant and explain to them that they are violating the lease and could be evicted if this continues.

Take ownership of your mistake and learn to do the proper due diligence recommended above😊

You might have to pay to keep these installed.

The quote includes the HVAC machine and installation.

The exposed walls certainly need to be properly insulated and sealed.

To make the most possible you will want it to be nice and inviting, also have a shower installed and at least a kitchenette IMO.Once you have your total cost for build out and furnishing, then figure out projected income. 

What type of floors did the contractor install? 

If you anticipate a possible fight, it's best to do things properly from the start.Certified mail in itself is not a panacea, in fact IIRC most of the relevant statutes say first class (i.e., "regular") mail - but it has to be sent under certain timelines.