I'd leave it as-is and let the buyer repair it, or have it repaired yourself if it's in the budget.

Take the time to learn how to talk to people, solve problems, analyze a deal, network with investors and cash buyers in your area.

The buyer had 10-14 days to inspect the property with a guarantee of 100% refund pursuant to Florida RE law. 

Usually go with non refundable down payment,  some type of monthly credit towards their purchase (only if negotiated ), buyer responsible for all repairs ( assuming home is in good condition when they are buying it) and if they are not able to execute at the end of the lease term offer an extension period with possibly a little more down payment. 

It's great to be a listing agent, the buyers agents do the bulk of the work.

As a first time investment buyer, I just don’t know which is the better investment.

They tend to be a bit stricter from what I understand, so some sellers might be less inclined to work with a VA buyer also.

Build better buyer/seller website2.

Has anyone bought preconstruction before, had success, or failed that could put some perspective on this?

You have to find lenders (and there are plenty of them in Arizona to choose from) that offer non-recourse loans where the solo 401k account is listed as the buyer (not you as an individual).