In your shoes I would not put the rentals in a business just to be able to put earned income in tax deferred or Roth accounts. Your real estate likely is already providing you with substantial tax shelter and you would pay FICA on the "earned" income and have other expenses you don't need. I'm much older than you and have pensions and IRA's as well as real estate rental income and I pay very little in income taxes. "Earned" income is never on the table here.
Instead, I would focus on investing in paper assets in taxable accounts that did not generate taxable events, such as high turnover within a mutual fund. I would buy low ER index funds and possibly some stocks that retain their earnings, similar to Berkshire Hathaway. Depending on the tax picture, I might add in some dividend paying stocks, as long as I was not giving a lot of that income away in taxes. As rates go up, I would also consider tax advantaged municipal bonds. In other words, investments that don't throw off a lot of taxable income beyond what is tax efficient.
You should look carefully at your current and anticipated tax rates during FIRE. You may find you can take some dividend income and capital gains and pay no taxes on those cash flows, especially early on, if you can stay in the 15 percent bracket. Two younger bloggers that write about FIRE and minimizing taxes with a high income are
http://www.gocurrycracker.com/ and
http://rootofgood.com/. They are both very knowledgeable and their blogs are good reads anyway.
