Really, you can use anything you want on the Darwin
Those cartos you mention will work just fine, the eGo stuff will work if you have adapters (either 510 extenders or a 510-eGo adapter, several vendors carry both), larger stuff like
tanks and whatnot may just require a single 510 extender to use. If you have cartos or attys on hand that are 510 (or any other type if you have adapters), then you can
throw them on there, no matter what resistance they are ;-)
Everybody's favorite gear will be different, so you can just stick to what you already know you like with no problems and then branch out to other things if you feel the need