Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

I would recommend them. 

May I recommend that you find a local businessman/dentist/doctor to fund your flips?

If anyone has a good starter spreadsheet or knows of a reliable website for deal analysis, I’d greatly appreciate your recommendations!

I would recommend to partner up with an experienced investor to really solidify your numbers.

In other words, I already have a checking and savings with BoA, but I would create a 2nd savings account (within my regular account) and put all the rental properties last months and security into that account (combined).Is this the correct way to prevent co-mingling of funds, or what would you recommend?

At this point, I would recommend having a line of credit to cover these things so you don't have money sitting in the bank doing nothing when it could be put to work.I have 33 units, no debt except for mortgages, and excellent income.

I use National Tenant Network to run a tenant score and recommendation.

Any recommendation for the first steps I should take if I want to purchase my first rental property using the BRRRR method (or flipping).

I'm also here to recommend Dainaird's new book on flipping.