Arda, Ea, and the Void

[Galadriel55]

For a while I was a bit confused what exactly do the terms above reffer to.

If Arda is everything that was created from the Flame Imperishable (ie everything within the Ekkaya), the Void would then be everything else. If Ea is literally everything, then it would contain both Arda and the Void. However, Ea is what was created from the Flame Imperishable, which means that the Void is not part of it. Then what is Arda?

I would really appreciate it if someone could untangle this knot for me.

By the way, another interesting question:

[Melkor] had gone often alone into the void places seeking the Imperishable Flame;... ~Ainulindale

Does this mean that there is distance in the Void? Wouldn't it make it not-a-Void, though?

My last question for now:

Far [Earendil] journeyed in that ship, even into the starless voids; but most often he was seen at morning or at evening, glimmering in sunrise of sunset, as he came to Valinor from voyages beyond the confines of the world.~The Voyage of Earendil and The War of Wrath

Firstly, where are the "confines of the world"? And secondly, how could Earendil travel into the Void? I thought it was forbidden... at least for ainur and elves, because they ought to stay in the world at least until Dagor Dagorath... and Earendil chose to be an Elf... Or is he just a special case, because it's the actual him entering the Void, and only for some period of time, and not his fea going to dwell there?