The simplest option is SEP-IRA, but it is limited in what you can contribute (20% of your net profit.) 

Sometimes the simplest responses are perfect and I appreciate the feedback!

It is probably the simplest way to get involved in real estate with no experience and still get a decent return without taking on too much risk. 

To answer your question,1) let me know if this is what you were trying to achieve.The easiest and simplest way to do this is:  - have each property(or few more depending on your risk threshold and situation such as different LLC for different State) under one LLC and have a rental contract for houses under the same LLC, keep a separate bank account and book for this LLC. and repeat the same with other LLCs. 

It never ceases to amaze me how come so many go to the effort of getting a great income, and great credit score, but forget the most vital ingredient that Lenders might look at: their savings record!

Subdividing land is the simplest way to make a profit on it.

Go fast on this one, all the ingredients appear to be there, just need to mix and bake, and deliver profits!

Simplest way to look at it is that industry averages are just that, averages. 

To build a fourplex it will probably cost me in the neighborhood of $500,000 to $600,000 and the best loan product I found is 85% LTV which is not bad but to be honest will burn up most of my liquidity so once I'm in this deal I would have to wait for a while in order to do my next deal.I feel like when things are too complicated they are not meant to be and the simplest things most of the time the right answer.

Yes, it is the simplest to propose, but the worst in terms of potential problems.