Get a builder quote from at least 3 LOCAL builders or Renovation Contractors first, then weight your available options. 

I understand if they are good they are busy, but I have lost one property so far and don’t want to lose another one.

Buyers still need to comply by their financing contingency terms, have an appraisal and structural inspection within the specified timeframes, etc. and could lose all of the money they put into those things, not to mention they're tying themselves up with a house that may not get sold to them.

Don't do a HELOC for long term just to have the tenant pay it off, that loses the advantages of HELOCs -fast cash, available any time, but floating/higher interest rates- Also, most won't give you a HELOC on a non-owner-occupied home.

Just know you could lose money if the market tanks between now and then. 

The sale price is such that we could sell in some weeks and not lose any of our investment in the purchase. 

Just to add...I'm fixing/flip in highly competitive Tampa Bay(Pasco/Pinellas) and one thing I've done that has shed light on what's happening when losing offers is that I've been keeping track of of each property from my offer to the actual sale.

I also know that I am in a tenant-friendly state and city, and even if I am in the right to charge them, I might still lose if they pursue it.

I’m losing my mind.

Do you have a weight limit on dogs to keep the potential "dangerous" breeds away, or do you find that most folks don't travel with their 100 lb Rotty?