If you meant more like what vehicle, I'm going to focus first on low end fix and flips and maybe do a house hack too.

The Reit or whatever investment vehicle that part does not matter as the principle is the same regardless.

Rent out your current house and invest that money by paying down the mortgage of the rental house or finding a new investment vehicle for your future.  

@Jeff Thompsonwhen you sell investment owned by the IRA - the gains are sheltered from taxes (because IRA is tax-deferred vehicle) and when IRA-owned investment produce income or cash-flow - it must flow into the IRA and also will be sheltered from taxes (unless the income is unrelated business taxable income). 

A 401(k) is generally the better vehicle, provided one qualifies for it.A strategy that could be used is the use of a 401k loan - i.e., a loan from the 401k - which can be used for any purpose.

I don't look at mutual funds as a vehicle to create wealth, but more of a place to KEEP existing wealth where you can get a modest return so your wealth doesn't get eroded by inflation over time.3.

Chris Mason  manufactures of Of these units by ALL means made multi family duplex units I have bought and installed many .. in Oakland no less.as long as they are affixed to a Permanent   foundation and removed from the motor vehicle registration they are considered stick built homes..

3) What vehicle would be my best option for this scenario?

It's a $35k car, but federal tax credits for electric vehicles make the monthly lease payment low.  

the benefit is that you can run multiple investments via your self managed investment vehicle.