Customer service is unresponsive.  

What would be my best route to take if we need additional finances?

You CAN limit that agreement to a specific property; but, as others have stated, agents are looking for a certain amount of loyalty from their clients.If an agent gets vibes from a prospective client that indicates that they want to cheapskate and not pay a professional for their service, they are not likely to waste their time with them.

I've got about $525K in equity in the property, but lenders have told me that I cannot get a HELOC to access that equity for additional purchases because the duplex was financed as an investment - they have said TX law dictates that HELOC can only be used on primary residences.

Additionally, I really want to dive into the property management realm and am passionate about connecting and assisting other Veterans and Active Duty. 

In addition to managing a diverse portfolio of rental properties, we've successfully flipped several properties in recent years.

Again, I’m not sure if these guys do this to everyone or if their customer service ability as partners is just terrible.

Prioritize deals that offer steady long-term returns over ones that seem too good to be true.DSCR Loans for Growth:Debt Service Coverage Ratio (DSCR) loans can be a game-changer for investors who want to scale.

I intend on sending the tenant a bill for the exact repair cost as "additional rent" (per the lease) instead of evicting in the winter and deducting from the security deposit.

Unless new companies create replacement jobs, the only remaining positions will be lower-paying service sector jobs.