No, the purchase agreement doesn’t need to be notarized – however, in some states (like Michigan, for instance), you technically need to get a witness signature to go along with each party’s signature (the witness doesn’t need to be a notary, it can be pretty much anyone). That being said – there’s nothing “wrong” with getting a notary’s signature on this, it’s just overkill.
At the showing, make sure valuables and other confidential items are put away so the potential buyers are free to walk around. Try and keep the number of people in the house to a minimum. Give them some time and space to look around on their own, but be available for questions. Gather receipts for heating costs, taxes, past repairs, or renovations; buyers interested in the house will want to know these details.
You can also look to certain companies and organizations that have a concentration of people that may fall in the above mentioned roles such as investment companies (i.e. Charles Schwab, Fidelity), financial advising companies (i.e. Morgan Stanley, Merrill Lynch). There may be a higher concentration of people who can both afford and want to build their own custom homes or to build income-producing properties. Try linking yourself to financial advisors who may already know of people who have these types of dreams. This isn't a comprehensive answer of all the possibilities but just some thoughts. Good luck!