Hey there @JJ Neerman, I know nothing of mobiles so I think Derek, Jayson and Micki are great resources overall.
I will chime in regarding sewer, septic, mound or lagoon, and wells, on the same property. I built and remodeled in the foothills of the Sierra Mountains in Northern CA for many years. Most of those areas were similar to your project and all I can say when buying existing systems is.....INSPECTIONS!
Have them both inspected by reputable LOCAL companies. And when you think you have ALL the answers, have them inspected by the next guy in line! There are distinct maintenance items for each, and if they have been neglected for any length of time, you could have a complete disaster an hour and a half after you close!
Hell, my own home was on a well and septic and even I didn't do ALL the things I knew SHOULD be done to properly maintain them.
Sounds like you are headed in the right direction and if nothing else it will be a learning experience! Best of luck to you sir....