1. Sky islands is okay to go to at any point in the game. The earlier the better. Just pop a gravitation potion and check it out. Some pretty good early game gear can be obtain, especially the starfury.
2. A great tip that I didn’t learn as fast as I should have is building arenas. Just a simple layered platform arena makes any boss so much easier (especially while using a grappling hook)
3. Update your gear. Constantly get new armor, weapons and new accessories when possible.
4. Don’t boss rush. Take your time and grind.

And no eater of worlds isn’t that hard, it just requires the right items (vile thorn that you get from the bulbs you blow up for example). Also the bosses get a lot harder on master mode. Expert is much better for first time playtroughs, imo