Fusions are not typically feasible until you are getting double chests on both UNM & NM every day. Once you are doing that, you will have a regular source of shards & gems.
Beyond that, you will want to be able to farm L20 in all of the OG Gear Dungeons. L20 is the most efficient stage for points/energy for both tournaments and Dungeon Divers. The secret sauce comes when you can farm L20 for each Gear Dungeon with 1 or 2 toons, which allows you to earn xp for food toons, which makes Training Tourneys/Events dramatically easier to do, and also allows you to level the rares/epics for the fusion for "free".
Spider & Dragon are the easiest L20 Dungeons to farm with food. Ice Golem is a little more difficult, and Fire Knight is the toughest because of the need to hammer the shield.