To get to Aleroth you need to talk to a couple people on top of the harbour building. There is no rush to get there, despite what Zandalor and Talana say (though there are a couple good merchants there).
There are flying fortresses where you can level (though you might want to clear the lower level opponents around the fjords first). In the original release of D2:ED there were anti-dragon shields there you needed to disable, but in DKS most were removed. There are portals for 3 of them in the fjords, one is spread out in Broken Valley and one you can fly to. The easiest fortress is Stone's (portal on the north east end of the island in the channel on the way to the fjords), then Raze (portal across from the harbour), then Broken Valley (though the mine is more difficult), then Keara (portal across from the Red Hammer tribe area) and Kali (end of the channel south of the harbour).
The shields around the harbour and High Hall can not be turned off. You can fly above or up to the shield and transform, but there is also a path you can walk, starting from near the depleted ore mine and eventually splitting to go down to the harbour or up to High Hall. There is a traveling merchant along that path that you only meet once, whom you can buy a malachite gem from and possibly good random items (farm for diamonds or make sure you have a lot of loot on you if you want to try to get most of his gold).
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