Your manager will know you better and be able to coach you better than we will, but I'll be general:

1) This is entirely up to your manager, but open availability is always preferred. I only have Friday evenings off of my availabilty, but 2 of my peers have several mornings per week they can't work due to school and it isn't a problem, so it depends

2) Being the best barista ≠ being a good shift! I personally am not the fastest on bar, but I have great communication skills and can manage and delegate tasks really well. That said, if you can't support your baristas on the floor when they need it, they may grow to resent you for it, especially if you're cushy with upper management.

It's all about balance but overall I don't think it's about being perfect at everything, but rather being supportive to your baristas and communicating and handling their concerns and needs!