I wanted the guests to know what to look for as they approached the property.

This decision not only maximized immediate profits but also enhanced positioning for future investment opportunities, demonstrating adaptability and a forward-thinking investment approach.

Always approach as a developer with a specific usage.  

You can check out their thoughts on how to approach seller financing here: Making Your Primary Residence the BEST Investment Ever (Better BRRRR!) 

You might approach your previous lender and explain the situation honestly but tactfully.

Developing that trust with someone you don't know may seem like a challenge, but if you approach it correctly, you should be able to achieve a pretty solid foundation of trust.The best way is to talk to others who have had an experience investing with the sponsor already.

This approach ensured minimal holding costs and a faster return on investment.

Very wrong approach!

So now I'm in a position where I can approach investing/landlording as a full time job if I want and try managing my properties myself, which is something I'd like to learn.

You'll want to talk to a local probate attorney to see how much time that could take.If the squatter is not making mortgage payments, you've got perhaps another month or two before the lender begins foreclosure proceedings.In your situation, I would approach the squatter to see inside the property to assess the condition.