When its included in a lease for real estate then the laws pertaining to residential rental security deposits in your state apply but when its separate you should have more leeway to get some additional deposit to protect you.

However the event of default just gives the holder or beneficiary of the security interest the RIGHT to accelerate all payments and call the note due..

Unfortunately, the husband lost his job about 8 months ago and, from what I'm told, hasn’t been able to secure another one—not even in retail or fast food.

For the past two years, my primary income has been my Social Security, and my home is fully paid off.

Consider all the things that could go wrong and see if the lease addresses them: unauthorized pets or tenants, early termination, security deposit, lease violations, late rent, eviction, lawn maintenance, parking, etc.5.

While both involve finding and properly securing a site and bringing it to full entitlement, the ground-up process includes the land piece but gets way more involved and complex to execute.The full "Monty" for ground-up development needs to include financial literacy, an explanation of metrics, and how they work.

The agreement is contingent upon the buyer securing financing which I was not able to do and have provided a denial letter.The seller is requesting money for damages because the appraisal came in at the purchase price but needed a heat installed in the kitchen which the seller agreed to install (Not in writing).

If your goal is financial security for your family, how do those things further or impede those goals? 

He is securing expensive debt, not debt through a bank, isn't putting any capital into the deal and structuring the equity investment in a highly risky manner without any upside offered to the investor.

It depends on a lot of factors; primarily the local jurisdiction rules that may limit lease changes (in Portland/Oregon rent, security deposit, screening fees, an no-cause evictions are heavily regulated).