2 weeks in Australia? First timer

Hi All,

I'm visiting a friend in Sydney in November. I'll spend the first ~3 or 4 days in Sydney, and have the other 9 or 10 days open. I'm not interested in visiting western Australia on this first trip. I'd love to see the Great Barrier reef, enjoy some beaches, I love seafood and nature. I don't plan to party since I'll be mostly travelling alone. Maybe some adventure to start followed by beaches?

What would you do with those 9-10 days as a first-time visitor? I'm not a luxury traveller. Please let me know if you have any insight. And, happy to share visit tips in return for Maine or Montana USA if you're ever visiting!

I'm from the US and understand how big Australia is, which is why I'm asking for help planning :) I'm aware 10 days is not a lot, but being from the US, we don't get time off like other countries...so please no "that's not enough time" comments

Cheers,