*Renovation Costs – Includes labor, materials, permits, and unexpected repairs*Holding Costs — Utilities, property taxes, and financing costs during the renovation time.

I'll be moving from California and only making a 50k  salary, but this job will cover housing and utilities.

Based on your post and other comments, it sounds like your rehab is extensive enough that the property isn't habitable.

To add value to the property, we undertook extensive renovations including the removal of over 40 yards of trash, installation of a new septic system and wall-hung boiler, and a new well pump.

You can tell that the lender isn't granting this extension under the provisions of the loan's 1-year extension options.  

My preferred options are:1. house-hack with a duplex under ARV; live in one unit => renovate => rent the other unit2. buy a SFH under ARV that could be converted into a duplex (preferably adjacent units vs top/bottom) - I'm assuming the biggest challenge with this strategy would be separating the infrastructure for utilities; and costly.

The plan was to utilize the HELOC as the down payment then getting a conventional loan to cover the remaining 80%.

Joint ventures entail utilizing your own money to buy properties with others.

Tenants pay all utilities.

I haven't seen anyone utilize an elevation cert to reduce the flood ins premium but it wouldn't hurt to reach out to insurance agents and see if it's possible.