Rank up one hero at a time. Start with Ena Hawkeye.
Ena Hawkeye is the go-to first hero to rank up. How far you take her depends on your server.
Rank Ena up to stage 1k (around Godlike).
Keep Ena as your main focus up to GalX, then move on to Kerth.
Use it once you travel with the portal. Set the portal about 1,500 levels below your highest level.
You may need some gold artifact levels; artifacts for the skill and for gold income help. A portal at a level ending in 434, plus 21 levels from the pocket teleportation device, lands just before a level ending in 456, where the special loot starts (every 1,000 levels).
Before anything that can give a rarity upgrade (the daily boss, Mythic or Big arena chests):
Your personal hero and Galactic X heroes do not count toward the 3.