I'd set up an IRA or other investment for exactly half the amount that I'd receive after taxes with my daughter's name on it that she acquires on her eighteenth birthday, or as needed for college. Eighteen years isn't much for an IRA, but I don't know of any other way to invest it at this moment, I'd obviously research it.
Then, I'd pay off my truck and make a few mods to it for the hell of it. A few inches of lift, more power, bigger tires, brush guard, and so on. Then, I'd pay off my house and buy one for myself. Next, I'd buy myself a small car and buy my girlfriend a brand new car of her choosing. Lastly, I'd find the best custody lawyer in the country and pay them whatever they wanted to work their ass off and get my custody of my daughter.