Can you rollover the expiring 5 year NISA to a new one?

The hope would be to then use that experience to set up a separate multifamily investment sometime next year using non-tax-sheltered funds and begin my passive income stream that way.To your point about self-employment, if I were to create an LLC for the existing properties I own, would I be allowed to start at least with the rollover, even if the LLC income wouldn't be enough to make significant contributions to the Solo 401K?

Then you would perform a direct rollover from your old 401k into new account. 

If I were you, I would close the old traditional IRA account after solo 401k rollover and just open a new Tra IRA for your backdoor conversion.

There are a few solo k providers who are very active on BP, so I'm sure those folks will weigh in here.Here's what the IRS has on their website about rollovers:Can I roll over my IRA into my retirement plan at work?

So, no, there is absolutely 100% no way your IRA could interact with you as described.There is a different plan structure commonly referred to as a Rollover as Business Startup that might work for you.  

SO, if put a little of my own money down, then finance the rest with a hard money/ private lender, how do I ensure I'm able to pull enough cash out of that house to pay off the investor plus financing and still have enough left over to roll over into your the deal? 

An in-service distribution allows a participant to rollover 401k assets to another plan (like an SDIRA) prior to separating from the company. 

You could make $2,000-$2,500/month in short term, low risk private loans for the time being, and then roll over your capital into acquisitions as they come up.

Can you roll over a 401k from a previous employer to get around the income requirements?