You might be interested to a look at hawker.social. It combines reddit with features of Patreon (subscriptions) and discord (sub channel). You can also use it as a substack style publication!
There is no contract so he isn't entitled to anything. To be on the safe side, you need to make sure that none of his work is used by the company. Eg redesign the logo. If you must use it, find a way to pay him for it. Form the company with just you and the existing IP asap.