You now have one pool of self-directed funds that can be invested with checkbook control.The Solo 401k cannot invest alongside you personally or your LLC - that would create self-dealing issues.The Solo 401k could flip houses, but you would need to hire contractors and remain at arm's length.  

Do you think I should be weary of these long term tenants going up in arms when I raise the rents?  

@Eric JohnIf your IRA owns the land, YOU cannot build a quad on that land.All IRA investments must be done entirely at arm's length, with no transactions or nexus of benefit in either direction between you and the plan.  

Bank A says after that it'll be 5-1 arms at 30 years Bank B says 5 year balloon loans.

With an ARM rate if I plan on cash out refinancing anyways within a year?

I honestly don't think I would go the one coin op machine route, but it is something else to consider and I love being armed with as many options as possible so thanks for passing the tip along.

Just make sure that all transactions that involve your 401k are 'arms length' and that there is no conflict of interest. 

You then convert it and keep it as a commercial 5 or 10 year arm with a 25 year amortization loan or refinance into a conventional 30 year loan with the increase value/equity built into the new equation thus a BRRR.

So I am a slow learner... but your post has given me a shot in the arm!

Hi @Paul Schackman,Only thing I'll add that no one else has explicitly stated: Two purchase contracts, two escrows, two down payments, two appraisals, etc.