Both lead to that buyer overpaying and taking an opportunity off the board for the investors who have their underwriting completed accurately.I believe its somewhat market dependent but it has become increasingly difficult to make construction oriented deals work in the price points you mentioned.

We are enjoying the park and the income continues to increase, as we improve the park.

Whatever increases the level of privacy on your rentals should increase it's value, possibly its rental rate. 

It appraised for 115k more than I bought it for so already have six figures in equity - will increase outdoor parking and raise rents over time.

Increased Capital Availability.

It sounds like a trainwreck on paper...and things usually go better on paper than in real life I would suggest saving, increasing your income streams, and learning in the meantime while you save. 

Biggest take away is permitting timelines continue to increase!

I'm thinking of offering $450K (cash and bank loan), make improvements as leases end, and then refi and increase rents as necessary.

Put up other collateral or increase your offer.

Its a 4bed 4bath, and the plan is to do a light rehab after the current lease ends, get new tenants and increase rents a little bit.