May as well stick to having The Golf Club as your sponsor, seeing as how you’re forced to start with it and begin making progress as soon as the TOUR starts.
You need to reach level 5 to max out the sponsor.
Pay attention to each difficulty’s objectives. If you don’t think you can get all three, don’t be afraid to drop down a difficulty. It’s better to get all three on easy than only two on medium, for example.
You should get this around your 20th/21st event.