Our best use for the property would be to build a couple of large estate home (8k sq' and up) and form a private estate, but, being that we are in the County with no existing zoning requirements, we could also build what we want and potentially turn it into an income generating property.

Half assed truths exists forever on the internet. 

You'll likely pay high premiums, face lots of claim denials due to "pre-existing conditions", and deal with service delays.

New to the BP forum and joined out of curiosity for a hypothetical scenario.I know everyone's situation is different, and everyone has different needs and priorities within Real Estate.So I was curious on one of the many situations one might find themselves in.In this scenario I wanted to ask if a HELOC on either your primary or an existing rental property out of 4 total properties would be a viable strategy for acquiring practically " turn-key " Multi-Family rentals?

So I'd be doing my best to get the highest possible rent/revenue but without needing or counting on that.What you refer as cut-throat competition exists in every market where you have demand.

The older the home and the closer to the city center, the less likely an HOA even exists. 

Fundamentals change neighborhood to neighborhood (i.e. appreciation potential), inventory/absorption issues may exist, rogue city council members and/or registered community organizations can make neighborhoods less appealing with little oversight which impacts value and marketability.

I'll add this, I think if you are good at it, there exist modes and methods which can give you much better returns. 

This way you can begin building your network (and even adding to your database of existing leads your current marketing campaign brings in). 

I do not have a lender right now, and I will need the 12-month rent history as well as various metrics on the property such as insurance quote (which needs property information in order to obtain), existing debt, and purchase price (which would be established while making offers).