Guild Donations are for the Seige Battles later on in the game & the 50 mil is what it costs to enter, if i remember correctly. this is why we ask our members to donate a sum from 500k to mil+. so min donation is 500k from lvl 50 say & from lvl 70+ you can donate either 500k or as much as you like. normaly the Donations are collected at the end of each month, this way it gives members enough time to get 500k. yes we do have an Account on Dekaron just soley for the collection of the money & this money does not get spent on anything other than the Battle Seiges.
hope this helps you