Advanced trainer here, and I'm wishing I invested in Superior right out the gate but mostly because I'm struggling to consistently get my rotation players to pop. It's still not that bad, but getting skills to pop takes 3-4 weeks at least. It's really a bummer to wake up on Friday and see that nobody popped at all. I live for that kind of dopamine so I'm trying to upgrade currently and it's VERY competitive! 600k-ish to get a Superior trainer with a good salary.
Your overall strategy sounds pretty good, though! I'd focus on upgrading your arena this season and invest in an Advanced PR staff member and try to keep that weekly salary as high as possible. You'll be competitive in a season or two!
Don't forget to drink water!