I don't know enough about any of that but I know there are people who can help you plan out your investments in their amounts, allocations and timing to maximize your returns and avoid taxes. 

Using partnership treatment to allocate SE income to the spouse with wages and away from the second spouse could produce a lower SE tax liability. 

The cost allocated overhead is divided based on number of units across multiple properties and added in.

So whatever your basis is in property R carries forward and is allocated into the two replacement properties. 

If I go to sell it in 2-4 years, will any portion of the property sale be allocated to rental use or does the 2/5 year use test apply here since I lived in the house before I turned it into a rental?

You'll allocate $2.4 million to $15 million by my calculations, with that range being the difference between buying 20 lots in the flatlands in the low to mid $100s up to the high range of buying 40 lots in the more expensive areas for $350K.Most of the lot buyers today are the big builders who intend to immediately build and resell, mixed in with a few end-users who are buying to build their own home. 

One of my IRAs has about 15k and I decided to allocate it to real estate. 

If you have 1000 in Marketing, I recommend allocating it to Big Data collection, and hiring VA's to Cold Call with you.

However if the LLC is a partnership for income tax purposes, then the LLC will have to track your built-in gain separately and account for this when doing the allocations / preparing the K-1s, which can get very complex. 

Many of us who live in expensive markets are constantly trying to allocate capital in RE, but struggle to find cash flowing deals.You might even have the income to pay off a good chunk of a mortgage, but you won't want to refi with raising interest rates, so does it make sense to purchase new investment properties with a "portfolio" of methods?