A profitable option would not only being a tax preparer but learning how to use Quickbooks then offering remote services where you do the bookkeeping of certain small businesses or even RE investors.

As far as book keeping, I will still keep records of everything according to individual property (for my own knowledge and in case of audit/ lawsuit/ etc) but, since I technically will be combining all the properties' supplies into one dollar amount reported on my tax return, and all the properties' repairs into one number, etc etc.. doesn't it make sense to just use one bank account/ credit card?

A little overkill, but if you don't have a good bookkeeper and you're not doing a lot of projects up front, I would do a new bank account for each project.B. 

or better ways of bookkeeping?

All the details of rent collection, leasing, maintenance, repairs and bookkeeping are handled by national class, professional property managers.

If you are buying with cash or bank financing, for the most part the depreciation is the same but you will have more complicated bookkeeping.

Well he doesn't just work with investors, he is an investor himself, and he understands that world.We use him both for our personal taxes, as well as bookkeeping and tax work for Nest Realty.

Tenants pay rent online, electronic signed leases, online applications (I still use Zillow for listing properties because I get better results) it’s my book keeping and it links with another site for sending out 1099’s.

It's a simple one page filing with an Articles of Organization and a small fee.Of course, depending on what you're using the LLC for, the Operating Agreement, bookkeeping, etc, could get expensive.

Note, you could run several businesses from one LLC (flipping and lending, in this example) and account for all income and expenses from one checking account.There are many bookkeepers that specialize in QuickBooks who could help you set this up and show you how to use it.