Yes, I did that for all the worlds up to Dragonspyre, including Grizzleheim, Wintertusk, and Wysteria. Eventually, I had to delete that character because everything was way too easy with zero challenge.
Yes. Of my 12 wizards, every one of them has done all quests in all worlds all the way up to the end of Zafaria, with only a few exceptions. Some of them haven't completed Tower of the Helephant in Wysteria yet, and others I'm waiting until they're level 90 to do the Aquila dungeons.
But Marleybone, including Kensington Park, has been completed by all of them... even the Warehouse, which you won't get until you complete Dragonspyre.