Specifically I think a lot about the smells that travel through the duct work between the units.

As you probably read through the comments on this thread, there are many moving pieces, costs, and folks involved in this transaction. 

I'm thinking HubSpot is the best choice. 

Once you have ran through about 3 months or so of this and penciled out 50-100 deals for fun, I would talk to a local agent and start the process of looking.

Once you have some baseline knowledge, the next step is to take action - that's the only way to build experience.

Unless you still want to buy the property, the seller is in breech for not closing because you are full ready to close but they haven't or refused to sign anything.In NC if the seller breaches, the buyer can sue for specific performance.

All the best!

How do you pay for the tax and insurance?

I would first check if STRs are allowed in the areas you're considering.

For example, if you invested $150,000 in a duplex and were able to improve it through renovations, attract higher rents, and increase occupancy rates, the value could appreciate more efficiently compared to a single-family home that doesn’t enjoy those rental income advantages.In essence, the key difference lies in how multifamily properties can appreciate not only through market forces but also through operational improvements.