It seems likely that working with a real estate attorney would grant access to contracts tailored to specific deals/transactions, along with other services that title agencies offer. 

There are often several versions, so ask experienced agents in your brokerage which are the 'bread and butter' docs used on most transactions.  

Because it's a cash payment, there is little proof of anything since there is no transaction history.

Section 121 on a portion of the house that is your personal residence.It also makes the whole transaction much simpler.

I've been concerned about how to cover myself in a transaction, but am now asking about if there is anything legally I need to do to be a private money lender. 

You are considered "disqualified person" to your 401k and assigning this contract to your 401k would be considered "prohibited transaction":https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-prohibited-transactions The proper steps would be:1) Establish and fund self-directed 401k2) Find and purchase investment

Ask yourself.. who profits more from a SFH Turnkey transaction - The buyer or the seller ?

I am held to a higher standard in real estate transactions as a licensee. 

Anyway a good thing for OP to be aware of.Here's the legal definition, it does seem like emailing properties would be a part of a series of events establishing procuring cause but just that action alone would not be enough to establish it: "In the context of a real estate transaction, procuring cause refers to actions that begin or set in motion a serious of events that lead to the final sale of a property.

There is no "moral" factor as long as all parties involved enter into the transaction voluntarily and with congruent, veracious information.