Take ownership and do everything by the book and you can get them out if you really do need it for your primary residence.  

If any property is being purchased or owned by a single LLC, the general rule of thumb how the file will be underwritten by a lender is anyone with over 20% ownership will need to be on the loan.   

For example, the seller would indicate that he/she is not aware of any adverse environmental conditions on the property during the seller's ownership.

The only way for you to take the ownership is to distribute the property from your IRA to yourself.

If I got a note and mortgage and did this, my 5% down payment would be made out in 2 parts: HOA assessments,  then the balance to the seller.There are different types of seller financing- a couple you get ownership via a deed like a mortgage or note and deed of trust, a couple you own nothing like a land contract or contract for deed (CFD).We have a hybrid CFD where we do get on title.

I have been advised by my title agent that the name of the partner bringing the cash to settlement for their 50% ownership should also sign the mortgage doc. 

All of the properties are under personal ownership, not LLC.$6.5M umbrella insurance sounds excessive and it's going to cost $3K per year. 

Once you throw in all the other factors you mention CoC is nearly impossible to calculate after the first year of ownership of a property.

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What baffles me about this recently is I see companies popping up offering fractional ownership of properties - I am always curious how that does not violate SEC regulations