I don't think you can purchase a policy for one tenant, but you can create a master policy for all your units.

If a person has RCV or ACV policy makes a huge difference, than question of what coverage level people had and if they had policy add-on's that cover cost over-runs and all that fun stuff, not to mention contents. 

I have home owners insurance should i buy another landlords policy as well?

This leaves $2600 after debt service (PITI).

How would an umbrella policy protect against a security deposit related claim?

Your primary strategy should be to have the Contractor and all Subcontractors add you to their insurance policy as Additional Insured. 

I'm excited to see so many of my peers in tech, prefab construction, government policy, architecture, et al come together to try to help those who need it!

What is PITI?

If the new administration actually enacts their policy stances on tariffs, immigration, trying to ignite the economy even more....all of those things add up to higher inflation.

That way you wouldn't need an extra policy.