I am under offer on a house built on a slope that already has an unpermitted 800 sqf walk out basement apartment and I am trying to decide if it's worth the money and time of getting the basement apartment remodeled and properly permitted as an ADU. 

However, the floors were done around ten years ago and the precise flooring can’t be matched.I was wondering if I should trust the management’s repair crew to do a proper job or whether I should make specific requests, as this type of situation is new to me.There is a cooperative tenant residing in the condo.Advice would be greatly appreciated.

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

I work in the travel and lifestyle industry in the Greater New York Area although I reside in the Northern New Jersey suburbs.

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 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? 

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.