Absolutely sure about the main quest thing.
I'm playing on the German server, too. There I'm staying with the same series of quests, as long as I want - just because I' m not making any move at my Main Quest. My friends here and on other servers do the same and it works perfectly. Here on Beta I deliberately stayed with the 3rd set of quests during more than 3 months, although I already had reached the endgame. Some of my friends have Main Halls Level 15 and still do the first series of sidequests.
So as long as you don't touch the main quest, the set of sidequests remains the same - however there might appear or disappear single quests.
LordB, you might test this with your little account. Leave the Main Quest alone, upgrade Main Hall to Level 15 and finish the tech-tree - and you will be amazed that you'll still have the 1st series of sidequests.
By the way, the first series is wonderful for acquiring cheap goods. On the German server I filled my stocks with 160 K marble, steel and planks. Now I' m about to enter the 2nd series and I plan to to the same with the 2nd - tier-goods using the 2nd set of sidequests.