The sellers are trying, like most, to protect themselves from the unknown, just like you.

You care for the health of the goose to protect the flow of eggs.  

What are some standard protections a buyer should look for once the project is complete?

You want to request a comparison with the same limits you have and then a quote with any changes they recommend.Because of differences in age, location, fire protection, limits, etc. you may find that splitting the two houses to different agents/companies may result in best rates but if its close I recommend putting both with the same company. 

There are ways to protect yourself from getting burned so if it looks like a great deal lets work it together.  

How would I protect my contract with him in case he shops it and enters into an agreement with another buyer at a higher price?

Cost a little extra but that ensures your friend is protected if something goes wrong.  

Didn't suggest any documentation I should ask for, just said it may be protected by a judge order for privacy purposes so I may not be able to get anything anyway.

If you ever need this entity to stand up in court or to protect you in some way, it would be best if you knew it had been set up correctly.Hope that helps.Ed

My wife and I realized, that after talking with several friends from the local REIA we should consider setting up an LLC for asset protection.