So for example; if you pay $500k for a rental and $400k is building value. 

Montgomery Metropolitan Housing has a reputation of being difficult to work with and are slow to pay at times r so I have heard.One thing to keep in mind is that even with section 8, you still get to set your criteria that tenants need to qualify for your unit. 

You do have to pay the seller the "equity gap".

Insurance would cover it, I would pay the deductible, and no assets would be lost.If you are in an area like San Diego where people are more likely to sue, a judge is more likely to find you guilty, and the payout is expected to be higher, you may consider an umbrella insurance policy.

You may be required to make estimated tax payments when the property sells.It depends on what your 2024 total taxes due were and 2025 estimated total taxes / withholding / estimated payments are.If you pay in atleast 90% of the current year tax or 100% / 110%(Depending on 2024 income), you are normally considered good.You may want to consult with an accountant for more clarification.

I am just starting out with a STR and found that VRBO is not very specific if they are collecting the tax and paying it to the State as a marketplace facilitator or am I responsible for this tax collection and payment ?

If they don't pay willingly, what are my options? 

Lots of absolute nightmares come out of sub to when folks get into title but dont have the money to pay the loan off or the ability to refi.

Paying this out of pocket is going to hurt badly after I've already lost rent for the past 6 months plus court fees.

I did not see marketing costs, nights that you need to spend at networking meetings paying for dinners or memberships.