They have to large military bases that leads to a high number of individuals looking for LTRs.

Owning rental properties presents an excellent opportunity to build passive income streams and create long-term wealth through property appreciation and equity growth.Furthermore, to explore various avenues for investing in the real estate industry, including partnering with other investors. i am open to Collaborating with like-minded individuals which allows us to pool resources, share expertise, and pursue larger-scale projects.

It's difficult to find info pertaining to individual investors with money to lend through brokers.

My recommendation would be to assess the entire neighborhood where the properties you're interested in are located, rather than focusing solely on individual homes.

You definitely came to the right place to connect with like-minded individuals who are well versed in the space.

Establishing an LLC for your real estate holdings can offer several benefits, especially when multiple individuals are involved in property ownership.

Indeed, it's not uncommon for such companies to sell slightly over market (whether selling individual properties or syndications or crowdfunded deals). 

How common is it for two individuals to go jointly on a mortgage for investment purposes?

#3 is the individual credible i.e. have they done what I want to do or have a unique perspective that will help me get to #1 faster?

Unless you can split off the SFR and sell it individually, it is significantly devalued by being coupled with the four plex.