The Hoarder perk increases your coin drops by 15% for subsequent rooms - so it is more useful to get it early in the run
The Croesus perk gives an additional 1000 coins and increases the coin bonus (calculated at the end) by 100% - for example, if there are no other bonuses active (BP/SBP, Player Appreciation Day, Coin Collection event), instead of +50% bonus for the last world you would get +150% bonus (and +100% instead of no bonus elsewhere)
For details on how this interacts with the Metal Detector, see Earning coins in Runs [Coming Soon]