This is by far the most important factor in my opinion.

Seems to be competing opinions on whether an LLC or other entity structure set-up is a must for a first time real estate investor. 1.

In my opinion, that shouldn't even be an issue.I apologize for not getting back with you earlier. 

I am sure everyone has an opinion about this topic, but I am surprised it is not more "front and center" on BP. 

But the best ways to get started are, in my opinion: 1) save up enough for a 10-20% down payment and then save a lot more on top of that for reserves, overages, and any unforeseen repairs.    2) have your financial house in order and have credit above 700 to get more favorable rate and terms from lenders.   3) speak to a loan officer that is experienced with fix and flips and get the necessary documents together for a pre approval (typically not much required, usually a valid ID, LLC docs if any, and two months of bank statements showing funds for down payment and reserves). 

Not a huge deal in my opinion and it may open the doors for more negotiations if i need to find other financing methods.

Not only will you likely find vary wide price differences for the same repairs, but you will also likely get differing opinions on what is causing it.  

Tell her if she doesn't stop immediately, she needs to find a new place to live.For the next lease, carefully about including someone's opinion. 

The property features two 1,400 sq ft suites on the main level (one currently leased) and over 3,000 sq ft on the upper level, with 750 sq ft already occupied, 3 small office spaces (+/- 250 sq ft each), and a basement tenant with 1,400 sq ft of storage space.The building generates $6,000 in monthly gross income from its five tenants, but with full occupancy and market-rate rents, it has the potential to bring in $10,000+ per month.Given its historical significance, stunning architectural details, and location, I’m curious about your opinion: Would this property be more marketable for sale with or without the current tenants?

You should wait until you see 5 to refinance in my opinion and use your income, which must be good, to work on an investment property.