Anyway, I know I should be researching properties so as in regards to using the Zillow app and just seeing proprietors for sale, should I call the agent and ask him questions about the property?

You can write off as a sole proprietor or partnership.  

Being a sole proprietor initially is not illegal, immoral, or un-american.

As others mentioned, there's really no benefit to doing business as a sole proprietor, so it probably doesn't hurt to do the LLC (other than the transaction costs associated with owning and operating one), but I generally believe that the protections afforded by these entities are way overblown, at least in the RE business, where individuals (myself included) are actively involved in the management of our rehabs/rentals.

I have a corporation, and I dread individuals and sole proprietors who send me 1099's for my company.

In this case, given he is a sole proprietor and not a full fledged company, there is likely isn't much recourse for us if he walks.

Anything I can do to my advantage tax wise / income wise vs. being a sole proprietor which I suppose is what I am at the moment?

I'm currently running everything under my Sole Proprietor business, but I know I'm going to need to change that soon.  

What happens if I just sell it as a sole proprietor as it sits right now and turn around and buy a rental property with the proceeds?

When you conduct business as a sole proprietor (meaning by yourself, no partner, no corporation or company formed), you are essentially telling the courts you agree to be held personally liable for your business dealings.