I would advise you to not spend your diamonds on anything other than expansions, at least for now.
update! i have fixed my issues with the page loading. iam resuming my duties tending to my city inDiamonds are best won as a prize from the Guild Expedition and horded until you need them for expansions, extra slots on your first Rogue Hideout, or for events with a prize that you especially cherish. Never spend diamonds doing daily challenges, negotations in GE, or any of the other myriad ways to waste them.