That will help you make the decision.Between your BAH and tax free 2 of 5 years primary residence you just have to breath to be a $1mm in 10 years.  

Hi, I am seeking advice on what kind of entity I should form for tax lien investing. 

We as a firm have investors working with us who have rental properties all over the US big and small.Finding a real estate-focused tax professional and one who can help with advisory and grow with you would be my suggestion to focus your efforts on finding.

I have used him for over 20 years and has been great but I want to make sure he is not missing any tax benefits for STR.

You haven't talked about taxes yet.

Property taxes here around around $10k/yr so around $800/month.

So far, I am in the midst of purchasing a couple of mortgages and I have purchased tax liens and deeds. 

I am also including the taxes and insurance while running the numbers.

Unexpected thing is actually coming from property tax rather than the performance of the STR itself, we still get 99.99999% fully booked.

.- Document everything (receipts for taxes, all the work that you did yourself via photos and video, and your expenses in an excel sheet to make sure you're on track.