I have been frustrated with multiple things that my current property management company has been doing, and I don't feel like they communicate very well with me.

If I was not starting from scratch, like I did myself, I would buy SFHs because I prefer their long-term flexibility, relative scarcity, and multiple exit strategies to MFH.

I heard about bigger pockets from a friend of mine that has successfully built and rented multiple properties in our area. 

these can produce good returns but best chance for success is for those that have experience in this area (I am a partner on an effort adding 8 ADUs, but it is not performing to the initial underwriting (underperforming) and it is an experienced team).good luck I get it, but not everyone has the opportunity of scale and building multiple units.

However, i would like a person with multiple rentals to help guide me to avoid some simple mistakes.

I think you should change PMs because you have multiple complaints.  

Don't split the work between multiple contractors if possible, finding one to do all or most of the work will keep prices down.Challenges were finding replacement pieces for certain items as manufactured homes were very different than stick built as well as going through state guidelines for affixing the house to the land

Would a bank even allow us to mortgage multiple buildings on a single lot without it being subdivided?

Call every local investor agenda (look at the agents that have investment property listings and call them) and call every local landlord that owns multiple properties (you can get lists off of Deal Machine).

The calculator is a LIVE excel with multiple tabs and all of them are interconnected, you may mess up a formula and you will see awesome returns inaccurately.