As such existing properties are often grandfathered in with their existing footprint, even if current zoning would require a smaller one due to lot size.

If the payment is conditional on the closing of the property, that's brokering and requires licensed agents.It can get sticky in my experience.One way is to pay for the leads, so its not conditional on the closing. 

For sure - seasoning requirement will only be 3 months which is generally equivalent to no seasoning for any real rehabs

A home is going to require minimum $300/month in upkeep costs no matter what (closer to $500 minimum in my experience, $5k-10k per year is what I have averaged in expenses on my SFR's over the past 15-20 years).

Needing a W2 job is not a requirement.  

I recommend you do this off platform because FF is clunky and slow and there are no penalties for doing so, unlike Airbnb- if it's a good fit for both of you, you proceed with whatever your process is (usually this will be an application, background check, lease, deposit)I say all this just to show that yes, it's cheap to list it there and in my experience it is VERY effective, but it requires legwork and follow up on your part.

Hello again – Does anyone know if we are required to keep our unused, decommissioned septic tank in the ground instead of having it removed?

This allowed me to proceed with the necessary rehabilitation of my house without having the required capital upfront.

No DTI required and low doc.

Depending on the physical relationship between the three lots, you may be able to remedy the situation with a lot line adjustment.