My background is a building inspector so my construction, code knowledge and credit score was a very unique skill.  

@Margot Baldwin It seems that both of you and your husband are in a great financial shape to have a comfortable retirement, however, to answer your question, I would suggest to find a financial professional who understands your unique situation, and help you plan your retirement properly, and your estate planning needs.

There are numerous options today; each have their own unique features but also similarities.Besides partial payments, what other features are important to you? 

Each tenant has a unique rent amount, so even if the teller does not make a note I know whose rent is coming in.If someone has your account number, they MAY NOT withdraw from your account (unless your bank does not have any security measures in place).I have a separate bank account for each building that tenants deposit into each month and I typically have a large balance in them to pay taxes, debt service and other monthly expenses, and I don't have any worries about those accounts being drained by some unscrupulous tenant.

They get a fair-ish rate of return with they added kicker of seeing how the sausage is made. 10% is on the lower side for a second position loan, particularity since it looks like you are cross-collateralized, but then again they get a unique educational bonus, which is hard to put a price on. 

The work I do is unique, fun, sometimes stupid frustrating but also sometimes rewarding. 

And there is no absolute answer and unique tool/strategy in anything real estate.

@Chris MasonProbably not relevant to your question at hand, but California is unique in that S-corps pay a 1.5% tax (subject to minimum $800 tax too).

Up-to-date on all the mortgage rates, terms and re-payment options available on the market.They only specialize in mortgages and are knowledgeable on current trends.They increase competition in the market place, thus keeping rates low.They save you time and money!

I am vaguely aware that sometimes a park can have unique "turf" issues that are different from the surrounding neighborhood and can be tricky....or maybe that is a myth I have fallen into from media coverage.