I currently operate as a sole proprietor. 

A cabinet painting business ran as a cash based sole-proprietor and I’m an insurance adjuster operating out of an S-Corp.

@Logan Kannes, if that LLC is also taxed as a sole proprietor then it is what is called a "disregarded entity". 

I am new to real estate investing, I have not talked to a lender for pre-approval because I am in the beginning stages of learning.What is the best business structure to use for a rental property business, Sole Proprietor, LLC , or corporation?

Sounds like this is possible to the transfer title of my property from me as the sole proprietor into an LLC to protect myself as long as I'm not transferring the loan into the LLC.

They normally run your personal credit report if I recall correctly unless you already accounts with them (I'm mostly sure)  That's why you can contact Chase for one of their ink business cards and say 'I think I'll make this much money' and i have a LLC or registered sole proprietor so please extend me some credit...however, I believe there are "true" corporate credit cards. 

Contractors are basically sole proprietors which means the plan would be sponsored in your own name. 

If our rental is owned in my spouse and I's name, do file as a sole proprietor or partnership?

You can open a bank account as a sole proprietor under your name. 

Loans are based off your net income if you are a sole proprietor like myself, so the more expenses I have, the less eligible income I will have for loan calculations.Does anyone know how small to large size companies get loans?