Those new quests will have to wait until after Sentinel Island in order to complete, so you can go there right away. One of the hallways on that level of Maxos temple (opposite the chamber with the bedrooms upstairs) had been blocked by a barrier, but is now open.
However, your first encounter on Sentinel Island you can mindread to go up a level, so the higher level you are (I made it to level 18 in the fjords) the more of an experience bonus that will be. You don't need to get to a high level, but it would be better if you got to a new level before entering, to get a full level bonus.
