Any person who guides you towards the success of your business can be called as a mentor.
1) A better way to find a mentor is , going to events/ meetups to build networks and relationships with people. Share your plans and ideas with people at there, from those relations you will definitely come across with some successful people in your business space.
Find out those people and ask them to guide you. if they like your ideas and attitude towards work, they will definitely show some interest to help you.
2) More over you need not to pay for a mentor.
3) If they said they want to invest, let them invest !! You can treat it as a first step towards the success of your business, why because they will show much more interest to help you when they have invested.
If they invested, you may loose some control over your business. But, don't worry about it. you can reach your goal some more faster.
4) People who are having some stake in your company can only sit in the board. until you wont allow them to sit, they cant sit.
5) They are just guiding you based on their experiences, it is up to you! weather to follow their decisions or not. But. If they invested in your business you have take follow them. But keep in mind!! what ever they do, they will do it for the success of your business.
All the best !!! and Wish you a happy new year.