I prefer using their money without the partnership arrangement.

The most common question people will have is “What are the sleeping arrangements?”

Additionally, partnership tax law for the more complex operating arrangements is often beyond the professional expertise of most tax preparers including most general tax practice CPAs. 

I will manage her Cleaner’s and be available to arrange maintenance, as needed. 

You can send me a private message to arrange a meeting.

That's a temporary arrangement.

However, we could make loans to a non-disqualified person who is also buying rental properties.So I got to thinking about a criss-cross arrangement...could two unrelated people building rental portfolios who also have substantial funds in their 401k or self-directed IRA invest in with each other?  

Most, HML are going with shorter term arrangements.

In your situation, if this sale involves the Seller (they see it advertised for whatever price, or if they live at the home and you have to arrange showings), you could be putting yourself in the awkward position of he/she wanting to back out of the contract with you if they know others will pay more for it.   

@Phuong DinhThe code section you refer to outlines Individual Retirement Arrangements, commonly referred to as IRA plans.The code allows for a wide variety of investments including conventional financial products as well as real estate, privately held stocks, precious metals, etc.Firms like Vanguard bundle plan administration services along with offering investments, and are generally limited to publicly traded stocks, funds, etc.Specialty firms offer what are called self-directed IRA plans that can be invested more broadly.