1.- Are there any other activities that give useful rewards? Like, any other lvl 80 zones apart from KoE? The patch notes mention something called Heroic Adventures but I've no idea where to start those.
Heroic Aventures are to be unlocked in the future, they are still locked to prevent the active up to date players progressing too much ahead of the newly coming players that are still learning the game. This way the devs allow new players to catch up on knowledge so we can all start gearing at the same starter line.
KOE is the only endgame zone for useful dailies to do.
These increase the spark lv you have that gives bonusses to certain gameplay aspects and are very good in longterm. Ctrl+l ingame for more info.
2.- I'm a bit confused because none of the enemies give almost any kind of loot (no gear or money). Repeatable quests give spark exp and those coins that you can use to get stuff in KoE, but nothing related to gear. And it looks like you have to do Distortions like 20 or 30 times in order to craft a single green piece of gear - am I missing something? I'm OK with slowly earning new equipment but it seems very limited and a bit boring if mobs only drop materials.
Mobs in astral, bosses in particular, are used to burn your astral keys. Astral keys is your only limited resource to gear up half you gear. They are being used when killing bosses, opening the boxes they drop. The gear crafted from these are the ones with a circling arrow when you look at your equipment UI.
Depending on what quality type of tools you use, you convert x amount of materials from those shards. There are always 3 different numbers given on the shards or dust, explaining how much you will gain for what tool quality you use, divided into these: worst; green tools ( anvil NPC) , average; Excellent tools ( AH/crafting profession/CS), best; Dominion tools (weekly reward from dominion ranking or Collector Editions).
The mobs in astral can drop astral gear as well but these are very rng, these DROPPABLE gears are the ones WITHOUT circling arrows, these are to be farmed from rng drops in astral, or to be crafted with professions.
You can also craft the astral keys type of gear with profession, but these are temprary replacers only since astral keys come over time. Then why use astral keys? The astral keys ones are stronger/better.
KOE currency is mostly aimed to improving your own maze (end of path of greatness), but most players use it to buy symbol of glories to boost their guilds.
Distortions are better to be done for dust farming in a more efficient way timewise, or farming insignia's to optimize your stats. Elsewise distortions have no purpose.
What is dust used for? Check the transmute tab at the anvil.
3.- Is the astral ship used for anything anymore or is it outdated content?
Astral ships are used on a daily basis.
They are used to do Anomalous Sector and Astral Hunt which are both required for spark lv progression. These are weekly requirements.
Aside from these events, ships are used to farm around in astral, kill demons, pray for good ship loot (cannons, shields, etc) and improve your ship that way.
If you have any more questions, hoping to hear of you