Also since it's a 4-unit it would need to meet the sustainability requirement. 

First, is it required by law for a buyer to sign a buyer's agreement before they start touring homes?

You'll have to meet higher ratio and FICO requirements. 

Quote from @Pamela Rivas: Hi Natasha,Here are some key points to consider about setting up a Mexican corporation:Setup Costs: $1,500–$3,000 USDOngoing Costs: $1,000–$2,000 USD/year (accounting and tax filings)Benefits: Tax deductions for expenses like maintenance, repairs, and managementBest for: Multiple properties or income-generating investmentsWhile a corporation is ideal for managing multiple properties, it’s NOT required to obtain an RFC.

Rent control measures, burdensome employment regulations, and excessive administrative requirements exemplify this.

Quote from @Jaren Taylor: Quote from @Stuart Udis: Depending on the transaction sizes you are pursuing, raising money to purchase property without debt requires either an incredible network of relationships or devoting a lot of time and effort to raising money.

Community banks generally have no seasoning requirements.  

So I’ve read that unbrella insurance providers require you to use them for car and home.

While having high standards is important, it's worth considering that many Section 8 tenants might not meet requirements like a 640 credit score or $90,000 in household income.

In CA, you are legally required to have a CA LLC if you are "conducting business in CA".