Welcome to FT!

Personally, having visited both, I'd go with Melbourne though the weather is likely to be a few degrees cooler. Bigger city, more to do. That said, Perth will keep you quite busy for a weekend. Items 2 and 3 on your list will be fine in either.

That said, you'll probably get more, and more informed, opinions if you post this in the Australia/NZ/So. Pac forum. Lots of real Aussies, not just Yanks who've been there several times, tend to hang out there.