The main issue is that to do the ADU you have to spend so much bringing other items up to code like electrical, plumbing, lighting (windows) and egress.

I am considering purchasing empty lots priced roughly $10-15K below market value.My plan is to offer owner financing for the land.These lots have water, drainage, and electric connections available, and mobile homes are permitted.The area is experiencing significant development, with the lots surrounded by new single-family homes.I would really appreciate any advice, feedback, or suggestions.Thank you

You can't lock them out of their room, turn off the electric, or anything like that.  

Insurers are looking at more than terrain, it's building, materials, electrical, plumbing, and roofs. 

Non UL electrical, plumbing &HVAC materials.

Not worth it to me.In my area if the pool has a powered safety cover that can hold body weight, then a barrier fence is not required.

Building a Compliance ChecklistA compliance checklist is a powerful tool to ensure your properties meet all requirements.

Learning how to use the correct tools and materials for a job, YouTube videos and even ChatGPT will help you get through 80% of the problems you will run into.My rule was I would not mess with HVAC, plumbing and electrical Or if it would take more than a few hours. 

I also have a list of all the other local meetups that I'd be happy to share...The super power I've found over the last 5 years or so investing is FOCUS!  

One very powerful tool is the built in analytics and graphs that Vrbo has.