What are some realistic expense figures that I can plug into my proforma to evaluate this property assuming it's properly managed?

If they are not hard wired, you may have to pay an electrician anywhere from $2K - $6k to wire them properly. 

I would like to utilize the HELOC to lend to the partnership, from my own LLC (which would be paid interest above what the HELOC charges) but am wondering what hurdles I need to jump through to do it properly.

I had to pay an engineer to do soil samples to see if the solid rock soil would support the weight of the addition.

I thought I had read somewhere that if you're month-to-month/holdover, the landlord can raise rent with no cap (at least the # of times) provided they give proper notice...unless that was the law *prior* to the bill being passed last year? 

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Cold call or drop-by on property managers, real estate brokerages, large investment companies, title companies, local lenders and ask what kind of help they might need at their office.If you like to be on social platforms you could probably get a job creating content for one of the above.I would put more weight on experience gained from the job than pay. 

By the sounds of it you are not seeking money, you gave proper 30 day notice the month to month would not be renewed past X date and you are now beyond X date and you want your property back. 

Additionally, I would post, call, and leave a message stating that you need to come inside the property to inspect with proper (our lease states 24 hours) notice.

yes, we have had similar situations and have not had any issues (SE MI) in gaining possession of property where the lease was properly terminated.