You will not break anything doing things out of the expected order. You will get less experience from lower level opponents for awhile (like Broken Valley, or in the depleted ore mine in the fjords if you have not been there yet), but the extra experience you are getting now will make up for that.
When you finish off Maxos temple you get access to a new area. Your first encounter there you can mindread to get enough experience to go up a level, so it would be best to leave enough opponents in the fjords to be able to level before going there, so you get a full level with the mindread (I got to level 22 in the fjords, so the mindread brought me up to level 23). Before that encounter is also a good place to do any outstanding mindreads that you may have, since the debt will be wiped out (and if you have any levels in Wisdom, by equipment bonuses or learning it yourself, that debt will actually get you a tiny bit of extra experience).
When my ranger was on level 13 I headed to the fjords and got to level 16 clearing down the mountain path and taking out a couple opponents on the far beach, then I went back to Broken Valley to clean up a couple outstanding areas and Maxos Temple (where I got to level 17). Back to the fjords, clearing the beach by the waterfall and swimming over to the beach behind the anti-dragon shields brought me to level 18, and clearing the path past the depleted ore mine brought me to level 19 (at which point I headed back to Broken Valley to kill a rabbit).
Returning to the fjords, the first level of the mine brought me up to level 20, and the remainder and then the first 2 opponents in the waterfall cave got me to level 21. The rest of the waterfall cave could get me half way to level 22, but all of the outstanding quests I had were not enough to reach level 23 (I tried, keeping track of how much experience each quest gave). I reloaded my save outside the waterfall cave and figured out which quests I would need to turn in to just reach level 22 when combined with clearing the waterfall cave.
