1. I don't think Morando's full invasion will be just that of Arcadia, but the entire world. He has a massive armada behind him, which could certainly work in the Part 2 finale if it truly is the end of 3 Below and/or the beginning of Wizards. The first part of the invasion, though, could definitely be Arcadia.
2. I don't remember those bounty hunters, but if they appeared once, they could definitely appear again.
3. I think that Eli will reveal his knowledge of trolls, aliens, and wizards to Toby. The trilogy teaser could definitely take place after Trollhunters and Part 1 of 3 Below, and for Pete's sake, it could even be the beginning of the first episode of Part 2.
4. I think Aja and Steve's relationship will grow stronger. It would fit if Toby, AAARRGGHH!!, Eli, and Steve become huge allies with Aja and Krel in Part 2 of 3 Below. Toby's the protector of Arcadia now, so this would be quite interesting.
5. Not sure, but I think if she does take one, it would look spectacular.
6. I think the Mothership might camouflage itself as a huge den or a cave, as those are natural formations with entrances.
7. I believe trolls will no longer have to hide from human society and they will be able to cooperate together.
8. I definitely believe this. Blinky predicted they would meet with Aja and Krel again, and if Morando arrives to Earth, then Jim, Claire, Blinky, AAARRGGHH!!, Merlin, and all those characters may return for the ultimate battle against Morando, which could take an interesting twist at the big finale of 3 Below and leave an opening for Wizards.
9. Yes, maybe. They might also be contacted by Morando to help him capture Aja and Krel, as both Kubritz and Morando have that in common. However, I think Morando could betray Kubritz like he betrayed Varvatos Vex, which may eventually lead to her redemption.
10. I think maybe. It may also be possible Morgana will break free of the Shadow Realm and initiate the apocalypse…