At my landlord's option, he can add 1 year to the lease, under the same terms (rent increases 3% annually).My landlord did not notify me the lease was expiring, nor did I notice.

If you lone  wolfed the deal and this was missed they can definitely keep the deposit. 

I'd like to create a contract and/or entity that will allow us to:define the equity split ensure my original funds are returned upon sale or refinancehold funds for capex and repairsdistribute positive cash flow on an annual basisdecide buyout clause in advanceWhere should we start on making this happen?

Then add you might save another 20 to 50k in private school fees annually.

@Libby Wolfe your name would have to be on the purchase agreement, so I'm not sure you can have total anonymity.

Make sure tenant is required in the lease to provide annual financial statements and store sales for the specific property so you can evaluate tenant financial strength. 

My plan has been to give 12% annual ROI and have unsecured loans from the investors.

Value of the property minus the land value divided by 27.5 equals your annual depreciation.  

I have perused a number of investment agreements which seem to be structured the way I described with a 36 month term, sometimes paid quarterly, though more frequently on an annual basis, but sometimes not until the end of the term.

Plus the upfront mortgage insurance premium and annual mortgage insurance premium can be pretty high compared to other conventional financing routes.