In my property that essentially has tree logs holding it up, there was later added some bracketing to secure the vertical log to the horizontal beam.

., the onus is on the contractor to make all the arrangements to get the material to the job; they can't point a finger at someone else holding them up because "you" bought the wrong/not enough material; who pays if they damage the material; if there is a material failure, the contractor isn't likely to cover the cost of their labor to repair/replace if they didn't supply the product; and so on.

Definition I found online - A due-on-sale clause is a clause in a loan or promissory note that stipulates that the full balance of the loan may be called due (repaid in full) upon sale or transfer of ownership of the property used to secure the note.

My real estate goal is to become a successful real estate investor in order to secure my future.

We have class A/B houses that appeal to those with security clearances and other professional incomes.

I also have more than enough reserves to comfortably stash 8 months of expenses aside in the event of vacancies.Since my investor is an older gentleman and looking to secure himself some passive income for a while, part of our private mortgage deal was that I can't refinance before 10 years, but also that I must refinance before 15 years.  

If you don't you've effectively reduced the security deposit you hold by $300.

I had a main supply line burst going into a duplex on a slab.

Tenants should always have "skin in the game" namely the security deposit.

I would remind him to clean and leave the property in similar condition as move-in for his security deposit to be returned.