It certainly was more difficult deferring property purchases until I could accumulate cash 15 years ago.

Whereas my other LTR rentals B,C,D,E etc, can accumulate/share deductions and losses , as well as carry over.

I would like to help them and don’t mind accepting half the rent this month, but I’m also wondering if I should mail them a notice of default just in case the late payments start to accumulate and become more and more delayed.

I would consider myself still in the growth / asset accumulation phase.

From my knowledge, security deposits should be in a non interest accumulating account so some kind of business account should probably be fine.

Capital accumulates and compounds so having more of it now will benefit you long term.  

He said if anything happened he could always mortgage the property and pay for medical expenses, if nothing happened he would have accumulated wealth.

This means you will spend 8-10% of your gross income plus leasing and renewal fees and accumulating deferred maintanance will make your investment less and less hands-off and your capital expenses will increase as time goes by. 

There is nothing wrong with being impatient and wanting to fill that urge to buy and accumulate more REI. 

The bulk of the proposal accumulates from 400.000$ to 1.2M$I'll contact you.