Hello Johanna,
First of all welcome to chronicles of arcadia.
1.) Mages are not popular at the moment. Every party needs one mage/warlock (support). If you want to play magic dps, warrior/mage would be the best option for you.
2.) I hope this can answer your question: How to earn diamonds
3.) Sadly they mean diamonds. Since diamonds on arcadia are the currency which gold is on other servers, its not a big deal. Like people had +999kkk gold in the past, now some people have +1kkk diamonds here. There is a little inflation, but the gold npc is more expensive now and diamond promotions got reduced. Dont be afraid, at the beginning its a little bit confusing but after 1-2 weeks you can handle this unique payment system here.
4.) Every character you create can be boosted once and get some startet gear for it. When i started here, i used the boost for my secondary class and started questing with my main class.
5.) There are many options.. the fastest and easiest way would be buying some cheap old stuff out of the auction house.
You can also do minigames like goblin mine and buy some equipment-items for phirius shells. Same for mementos, proof of myths or arcadia coins.
I hope i could help you. If you have more question just pn me here or wsp Røflcøpter ingame.
Best regards,
Røflcøpter