I have a wholesale contract that I drafted that needs reviewing/revising.Any references would be greatly appreciated!

Is there a contract for this.

I was provided multiple contracts but was recommended to seek a Real Estate Lawyer to look over the validity of it.

http://www.nolo.com/legal-encyclopedia/maryland-form-llc-31870.html It goes over the requirements to set up an LLC in MD. 

I co-own a contracting business that has done rehab projects for other investors so anyone interested please contact me.

And if they don't exercise the option by the end of the contract, all that money is no-refundable.

This all of course could be done via contracts but it also seems a bit messy, granted anything other than seller financing is going to look messy anyway.Any thoughts on this vs seller financing would be appreciated.

Is it possible for a property zoned Residential (R20) that is legally conforming to have a highest and best use as commercial via an appraiser?

First, we don't know what your assignment contract or the purchase contract says.  

If they own several they are obviously investors.Once you get a response from the seller of the vacant house, negotiate a deal to buy it for all cash and get it under contract.