Hi Clare!
The jewelry on your site puts to shame the web design work any of us here would do haha.
Not sure if you've found someone to help you yet, but figured I'd take a shot anyway.
I took a look at your requirements, and managed to fix (locally, on my computer) #s 1 & 2 in about 15 minutes using Google Chrome's developer tools, where do I access the donation drop-down in your shopping cart?
Cheers,
- Kevin