I recommend that they setup an LLC and when they expect their net earnings to exceed what a reasonable salary is for agents in their region, then I recommend electing to be taxed as an S-Corp, so that they can set their salary to the reasonable amount and fix their SE tax at that level.

I would put a priority of finding an accountant who specializes in real estate taxation over one that is local.There are 20+ accountants on this message board who specialize in real estate taxation.

Agree with the details above BUT for buy & hold rentals I also look at the operating costs, Capex & esp depreciation recapture (taxation), as that can be a sobering realization on what the 'final' equity is after a future disposition.

It will be difficult to generate those kinds of returns in your own small multi-family without leverage.I think you are overstating both the cost and complexity of taxation on Unrelated Debt-Financed Income. 

If you do need to file and pay sales tax, you can do so with the Ohio Department of Taxation here.

It allows you to claim the rental income at a lower taxation level and also validates your tax position of being a "full-time real estate professional."

- how you ensure my proposed structure is accurate, flexible and relevant, so that aren’t any things that will come down the road and increase my taxation, or possibly hurt overall ability to further engage in business planning? 

Couple of things for you to consider.If you're thinking to move as well you'll want to take a look at state taxation. 

You not only have to be concerned with "THE MAN" (IRS), you have to be concerned with "the man" (State taxation). 

With the recent increases to standard deductions - the taxation benefits of owning your own home have been reduced.Being a landlord continues to be tax effective.I have a family member who is looking to buy for themselves personally - but I am helping them with down payment.