Since this was out of my experience I hired a "Structural Engineer" to replace all of the rotted out studs, reframe the wall, and a few other things.

I'd be open to a month to month lease, but I'd still have them go through same screening, same deposit process, and same rules as other tenants.

If you have a similar structure, can you please suggest the bank that you went with to open Texas LLC account?

Check out Zen Business for forming an LLC it's pretty affordable and has a "pay as you go structure" They have a registered agent you can get as an upsell for instance.

And/or any advice on when it's the best time to drop that kind of coin on structure set up vs. just having a couple LLCs in the beginning. 

We are able to do short term rentals with the other unit and learn many skills throughout the process. 

That can lead to odd quirks, sometimes good deals, and sometimes long and arduous processes, it just all depends.I will share a story - one Credit Union was offering such attractive HELOC terms that Auto Dealerships caught on to it.

You'll need a lawyer to generate the paperwork and filings and experienced enough to give you general advice on the process, help you establish appropriate compliance and back office procedures.

They then finally turned in the schedule c over a month after the deadline, which I couldn't even utilize as my independents had already filed and would not go through the process of paying extra to their accountant to amend the filed taxes.

A lender I'm currently working with said their underwriting process is taking 60+ days right now and he started me almost 3 months out.