What two federal agencies oversee regulatory requirements involving residential real estate?

How feasible (in terms of timing, getting regulatory approval, etc.) is it to either expand the property's floor plan or build 2 units on the property?  

Never mind the operational, research, regulatory ect skills required.

Answer that first.STRs- Too much regulatory and market risk.

Aside from constant threats to drastically alter the property tax structure, existing and expanding rent control, anti-landlord regulatory environment, anti-landlord/investor public sentiment, litigious tendencies, liberal judges, tents popping up everywhere, cardboard sign carrying panhandlers at virtually every roadway intersection, trash on roads pretty much everywhere you look, increasing crime, high cost to get pretty much anything done, and not the greatest economics (speaking from an investment point of view such as price-to-rent ratio, etc), probably my biggest reason is that I like to invest in places where people are moving TO, and avoid places where people are moving FROM. 

You could originate what you thought was a business purpose loan that turns out to be a consumer loan, thus leaving you with multiple state and federal regulatory violations ... ever hear of a flipper that underestimates the resale value and moves into and lives in the house?

ValuePenguin is a good source for the relative cost of insurance by state.Operational Costs - Costs like property taxes, insurance cost, state income taxes, regulatory costs (ex: time and cost to evict), inspections, rent control, etc., have a tremendous impact on your return.

They are a regulatory body of the executive branch of a state's government.

Does anyone use RUBS, and if so, is there any regulatory requirement with PSC or DNR?

How familiar is your company with the regulatory environment for rental properties in California?