First you must determine if you want to purchase the service station operating business and lease the real estate, purchase the real estate and be a landlord to the station operator, or purchase both the operating business and the real estate.Many of the best locations are either owned by oil companies and leased to operators, or have restrictive contracts with severe penalties for changing gas suppliers.  

However, she stated that the old management company is still working the property, but the contract has expired and they never signed a new contract with them.

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.

You're going to sign a contract to buy the property from the bank, so I doubt you're going to be able to wholesale it to someone else. 

We plan to speak with real estate attorneys on all the legalities, but I think it'd be helpful to hear from someone who pursued this successfully in Illinois.

The question I have is:Once the tenants sign a 1 year contract and then I purchase the home. 

We have a duplex in North Haven under contract  and a SFR in Branford rented.

Before you do that I would find out what legal leg you can stand on, be it your lease or some local law you can point out.

Are you going to form a legal partnership or LLC?

If the situation seemed bad to begin with I might add that into the contract.