Of course being able to move the money from the 401k to a solo 401k or SDIRA, the 401k would have to be from a former employer. 

If you need to use them against your w2 active income, you need to be a real estate professional.

Accountants are in such demand, that the best are not even accepting clients half the time.The other problem I see often with accountants on here is that they specialize in larger investors, and have really high prices when you as a smaller investor do not need all the bells and whistles.Another thing I see is folks thinking they need to have a tax professional in their state.

Meaning at what point do you hire employees, quit other income streams etc… Is the money coming through cash flow from rental properties or buying and selling… I am 21 and just starting out and this of course is the plan for the next 5-10 years but I want to plan ahead.

Of course, I stay on the merry go round and do it again, but it works a lot easier with CS & BD. 

Realtors, for instance have deep knowledge of the market and will mostly have a network of trusted professionals they've built through successful collaborations.

Of course, with private lenders, you will need to give up equity or a return on the debt.Hope this helps! 

Main challenge is financing (but pushing me to learn more about creative financing) Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

Rental per room will be always more profitable than as a whole, depending on the market of course (rural vs urban) check local listings for comps.

Acquisitions of course can typically be OK as vacant.