I haven’t started a yoyo company so take what I say with a grain of salt:
-Name
-Logo
-Mottos are nice (not necessary)
-Have direction: know why you started this company and where you want it to go. Without this you are not a company, you are just someone who makes expensive toys.
-money (of course)
-well thought out yoyo designs that actually work! (very very important)
-either you need a person to make the yoyos for you or a lot more money to get the tools to make your own.
-good relationships and contacts with people in the community. These people can help in so many ways. They can help guide you or directly help you with things from machining, designing (the art and yoyos), retailing, wholesale parts and materials, and so on
That’s a small list of random things I could think of! 