Here's a list of expansions in order of level/sequence:
Celtic Rift: "Recommended for low level characters and start a new character to fully enjoy."
If you are just starting to play The Quest, take your new character to Celtic Rift from the port at Matras ASAP. You can just create a new save and keep one in Matras to continue the main game and the other expansions. Celtic Rift is considered its own continuity, and you get items there that are rather game-breaking outside of Celtic Rift. A new expansion, Celtic Queen, is coming in a few months and will continue the plot, so hold on to your saves in the Celtic Rift.
Cursed Chess Set: "Recommended for low level characters."
I recommend you gain a few levels and complete a few quests in the main game first. You don't get too much that is game-breaking in this expansion, and it is a good idea to have your bearings about the basics before going there.
Islands of Fire and Ice: "It is recommended to reach at least level 14."
Just make sure you aren't at too high a level when you go here.
Hero of Lukomorye I: "It is recommended to reach at least level 22."
Hero of Lukomorye II: "It is recommended to reach at least level 32."
At this point, you'll probably want to create a new save so that you can play Mithril Horde I-II without being over-leveled!
Mithril Horde I-II: "It is recommended to reach at least level 35."
Hero of Lukomorye III: "It is recommended to reach at least level 38."
Escape from Asteroids: "It is recommended to reach at least level 40."
Hero of Lukomorye IV: "It is recommended to reach at least level 45."
At this point, you'll probably want to create a new save so that you can play Lost Archipelagos without being over-leveled!
Lost Archipelagos: "It is recommended to reach at least level 45."
Attack from Asteroids: "It is recommended to reach at least level 58."
Hero of Lukomorye V: "It is recommended to reach at least level 61."
If you play the expansions in this order, playing the main game in between for leveling, items, quests, and such, you should be fine. Hope this helps!
