If you have a small and/or basic unit I think it could be looked at as optional. 

When you have control of your budget, money saved, and enough knowledge to be dangerous, take action!

Though, you would need to put down 10% in which their fees can be a little high along with a 10-12% interest only rate.

2) Also, is it allowed for proceeds of both sales to be used as down payment towards 1 single asset?

Be patient. these are mid-term plays, so you must be prepared to go without the cash for several years.

You are going to be thousands in the whole before you ever start and any cashflow you get from a rental will be eaten up in tax and corporate filings.

We plan to be in this area for foreseeable future. 

Costs of set up of Trust, Costs to attorney to set up note, monthly costs to service the mortgage.Just my guess.My thoughts are if you have reached the level of a trade or business, then yes, these costs would be deductible.

To that end, I would find your local REIA meetups so you can also connect with your local market as well.  

Since refinancing and investment income (like rental income) usually aren’t seen as earned income, it likely won’t affect your mom’s survivors' benefits.However, if your mom’s survivors' benefits are based on disability (SSDI), then additional financial or property assets could trigger a review, so you might want to consult a CPA or financial advisor to be sure there are no unintended consequences.This isn't legal advice.