Most, if not all, State landlord/tenant laws will prohibit limiting the landlord liability by having a tenant sign away their rights.

If the condo or townhome association prohibits or limits rentals then you cannot rent the property. 

Unless the equipment is old, upgrading working equipment to more efficient is cost prohibitive. 

Also, if the real estate is owned by you, it cannot be exchanged to the IRA or solo 401k as that is considered a prohibited transaction.

Unfortunately for many, short term rental permits are now prohibited for homes in R-1 and R-2 zones.

As a property manager I can tell you that fair housing prohibits you from charging pet rent or requiring a deposit.

So if the business that adopts the plan is the GC for that house and uses the money from the solo k  is that a prohibited transaction or would I need to hire a different GC to use that money?

My landlord policy prohibits day cares.Whenever people ask about day care, my answer is no, even when they offer me offer extra money.

Conducting business with disqualified persons will result in a prohibited transaction and will disqualify your IRA resulting in severe penalties.

Here's what it says on the IRS's website involving disqualified persons:Prohibited transactions in a qualified planProhibited transactions generally include the following transactions: A disqualified person’s transfer of plan income or assets to, or use of them by or for his or her benefit A fiduciary’s act by which he or she deals with plan income or assets in his or her own interest A fiduciary’s receipt of consideration for his or her own account in a transaction that involves plan income or assets from any party dealing with the plan Any of the following acts between the plan and a disqualified person: Selling, exchanging, or leasing property Lending money or extending credit Furnishing goods, services or facilitiesExempt transactionsThe law exempts some transactions from being prohibited transactions.