Definitely look into STR regulations in any area you're researching.

Also, based on the new regulations (1 of the 2 units must be owner-occupied), how do you think this will impact the home's value?

Too often we see Landlords keep rent down to reduce headaches, only to find out later that they can't raise rent due to rent control regulations. 

My question is, can I use one of the separate parcels as collateral for a construction loan to build a multifamily on it (of course adhering to zoning regulations)?

Understand Local Laws:Familiarize yourself with local landlord-tenant laws to ensure you comply with all regulations.

Quote from @Heather Rummel: You can manage it on your own, but it takes a lot of work to educate yourself, particularly in the most heavily regulated corner of the world.I would start by calling around to property managers in the area for help.

Start by checking into regulations.

For all loans, amongst other things, I have a recorded Mortgage/Deed of Trust, Promissory Note, and Personal Guarantee in place.Yesterday, out of nowhere, my bank reached out to me and asked me if my business was regulated. 

My guess is political noise is going to spur action with both the CFPB to regulate these transactions and with investors calling the loans due. 

My out of date layman's opinion is that if the building ever had six or more units what you'd wind up with is one deregulated apartment and four regulated units.