a vapor barrier is a must behind the lap siding

I used to have difficulty in California converting garages because of the lack of Steel/Concrete PSI/vapor barrier.

Garages are not built as living space, the main consideration being the slab and it's lack of proper rebar, PSI, and vapor barrier.I've been asked to have the slab X-Rayed to prove that it was up to current codes.

You could yes, because Tyvek is breathable and not considered a vapor barrier. 

FYI: The repair work is crawlspace/vapor barrier/sump pump/dehumidifier and outside drainage along the house and hurricane windows.If I form an LLC, will I need to re-finance with a business loan?

If needed, add a crawl french drain, sump pump and 6 mil vapor barrier. 

Principal risk is vapor intrusion (vapors from groundwater migrating into buildings) or contaminated groundwater if used onsite.

My wife is thinking to put a plastic vapor barrier over the dirt floor and to cover with rubber mats? 

So far in that unit, we've had leaking toilet seals, a backed up washer pipe (crushed or corrupted by roots somewhere underground) that we rerouted into the main exit pipe with a pump, a completely stopped up sink drain, and water coming through the vapor barrier causing rusting on the cracks in the vinyl floor planks.

Down Payment - $17,700 (20%)Closing Cost – TBA (estimate is $6500)The property is currently occupied by a tenant, we do not have an appetite to keep them in place for a couple reasons We don’t want our tenant to know more about the house than we do.We have read Brandon’s book on managing rental properties and feel that we need to take ownership of     the tenant screening process and develop real skills in this area.The tenants are a family friend of the current owner and the rent rate is way below market rates.During the walk through we noticed there is a spongy floor in the hall bathroomIt seems there was/is a leak associated with the bathtub and it has caused damaged to the subfloor, joists, etc.We have had the termite inspection completed and after talking with the termite inspector here are our key takeaways.We start with getting a termite treatment in place to resolve the one small termite trail they found.The seller will pay for this as we made the contract contingent on getting a clear termite letter.Next, we need to verify the cause of the water damage has been fixed and will not create additional issues in the future3rd we need to make necessary repairs to the joists, subfloors, etc in the hall bathroom.4th we need to clean out the crawl space underneath this house5th We need to replace the insulation and old vapor barrier underneath the house.6th we need to install vent wells for the vent ports outside the house.With tenants still living at the property it is very difficult to get access to the house during this time period.As soon as we have full access to the house our plan is to do very systematic walk-throughs and start building a punch list for repairs.We have multiple people involved in this industry who have offered to come do walk-throughs with us and provide suggestions on items we should fix and how to fix them.Our plan is to do 3 or 4 walk-through's, build out a line item punch list and then start prioritizing what needs to be fixed.We plan to support these punch lists with photos or videos as appropriate to help speed up getting quotes from contractors.Because this is such a small house (1125 Sq. ft) we feel we can keep our rehab costs reasonable.We plan to be very involved in the rehabbing process in order to save money but also to gain experience so that for future projects we have a better understand of what we don’t mind doing and what we know we want to contract out.Next Steps Closing is first week of March, 2020Working through the financing process right now with the same bank who is refinancing our primary residence.Trying to get organized and prepare ourselves to get the rehab finished ASAP.I plan to make weekly updates on this; any feedback or questions you have would be great.