I'm thinking about investing into section 8  housing in STL and I'm new to this game.

Wow, what a rollercoaster 2024 was for the housing market.

I and my spouse are planning on buying a small multifamily and house hack.

Non-passive to achieve this level of return.Add the addition of the ADU makes the main unit rent controlled if over 15 years old.the work to add an ADU likely exceeds the effort of a brrrr that can achieve infinite return  Experienced investors are adding multiple ADUs by leveraging items like bonus density, committing units to affordable housing, etc.  

I have done quite a few different things, one of the best to find out who is doing the most volume is go onto good and search for the "we buy houses companies" in the area you are looking to invest.

I first started out in Real Estate by house hacking in college. 

Leverage your construction skills for flips, start with smaller projects to minimize risk, and consider house hacking or long-term rentals for a steady income.

Does anyone have a good effective 3rd party mailing company to send mailers direct to seller?

I have some in-house laborers for any large projects but sometimes value add can even be raising rents to market or finding an off market gem. 

I recently came across a property through an agent with attractive numbers for a house flip.