Whether you do all the blocks the same or different IS a personal choice. If you bought a bunch of these fabrics, you might want to do all the blocks the same - just to use up your fabrics. And that has a more "formal" look. Personally, I like a scrappier look. Your block has blue, pink, brown, and lots of greens in there, so I, personally, would make stars in all those colors. To me, scrappier quilts "sparkle" more and look less formal. Maybe keep the fussy cut centers the same for continuity. You're right about a straight set - because of the fussy cut center. And I wouldn't decide on a sashing color yet. Wait until you have your blocks made, then audition different colors right there in the store. I often lay out a bolt of fabric on the floor of the store and lay my blocks on it with an inch or two of the bolt fabric peeking between the blocks. Stand back and squint if you have to. Usually, I'm surprised at what works and what doesn't. You might get funny looks in the store, but it's worth it for the right fabric.
Hope this helps and have fun in your class. Your block looks very nice. - Tina