You make book keeping easier and can show the LLC is making money. 

If you're looking for maximum scaling, I'd recommend outsourcing your bookkeeping to a professional real estate bookkeeper or a CPA who offers this service.

(I know good bookkeeping is a must in any situation) Thank you!

Honestly, there is no to little need for the separate set of accounts you have now unless your State requires it.It won't matter iIf you have a bookkeeping arrangement in place to keep track of your income and expenditures. 

Im a realtor, I work at a property management company, I have network of commercial/residential/private lenders, a list of contractors, a phone book of other investors who are doing the same things we are, a couple good attorneys, a book keeper, and a killer accountant.

Would I need to issue a 1099 form to my girlfriend for bookkeeping / turnover maintenance throughout the year (well over $600) if I own a few units?

You may be the only one in your company but you need to subcontract out items such as maintenance, evictions, bookkeeping, leasing, etc. you may be able to handle the bookkeeping and the leasing right away but after you get enough units you want to hand that off to other people.  

If I could go back in time I would definitely get a book keeper involved ASAP (assuming this will be done through an LLC).

I think good book keeping is the proper solution.

Other software has rent collection and tenant screening features but focuses more on income and expense tracking and report generation (so is more useful when it comes to bookkeeping and filing taxes).