What to do with money?

Two options:

1. Become an investor in SpaceX. $10M is not enough to start your own rocket company (it takes at least $1000M), but it would be enough to be taken seriously as an investor in another company that has a record of success, yet still needs cash.

2. Become a subcontractor. Build something that a larger company doesn't do themselves, but might be willing to buy from you. For example, one could start a company that makes space food.

Citing comments of @Tristan and @Polygnome:

$10M will pay ten people pay and benefits for maybe 5-7 years. That doesn't leave any money over to get any hardware.

Well, Elon musk invested about $100 million from 2001-2006 of his private money into SpaceX. Falcon 1 would not achieve orbit until 2008, and that has only about half a ton worth of payload. That should give you an idea.

I would add to them, that although $10 million is not enough for orbital rocketry, you can still join an already ongoing private rocketry project as a business partner or as an investor.