yorktown1983: i am lvl 23 and barely in skellige!! i played advancing the story slowly trying to do all the sidequests. so now i dont know do i advance the story so i can do more quests w/ wolf gear or not?? 
  Sure, why not. You're not pegged to a single map, so you can go back and forth whenever you want. So far here is the order I've played my game up to level 28:  
 White Orchard 
 Vizima 
 No Man's Land - Velen (all over) 
 No Man's Land - Velen (Oxenfurt) 
 No Man's Land - Novigrad 
 No Man's Land - (various locations finishing up open quests) 
 Skellige - Ard Skellige - (main island + various ? in the water surrounding it) 
 Skellige - Hindersfjal - (quests + ?'s in water) 
 Skellige - Faroe (quests + ?'s in water) 
 No Man's Land - Novigrad 
 No Man's Land - Velen (various locations for side quests and other that I wasn't high enough level for previously) 
 Kaer Morhen - (main story, various scavenger hunts for wolf gear and all side quests, everything I was able to do) 
 Novigrad (sell off crap from Kaer Morhen, do a few more quests) 
 Skellige - Ard Skellige (main island few minor things) 
 Skellige - Undvik - (Marlin Coast briefly) 
 Skellige - waters (random surfing for sea loot, stumbled upon Isle of Mists by accident apparently) 
 Skellige - Spikeroog (currently where I am now)  
 You can quite literally hit up a fast travel post and go back and forth any time you want. I favour doing as much as I can on one map before moving on to another as it's more immersive that way, but some quests open on other maps end up way overdue then too, so I swung around to knock off some of them a few times. Just do whatever seems fun, and if you don't want to progress the main story line just avoid doing the actual main story quest until you're ready to move on. You can still visit any map though for side quests and exploration, just don't trigger any main story stuff until you're ready to.  
 My current plan is to do as much as I can on Spikeroog, then patrol the waters all around the area to see everything there is to see both in the water and on the billion smallish islands around there, head back to Undvik to do the quests there and in the water around it, then on to An Skellig for the same, possibly hit up the main island if there are any undone quests I'm leveled up enough to do. Then I'll likely be off to Novigrad/Velen again to do a sell off and complete any other side quests I'm powerful enough for before getting back to the main story line.  
 That's my general game plan anyway but subject to change based on whatever random crap happens in game. :) One thing is for sure though, is that I wont have to worry about being kidnapped in my sleep by the Dark Brotherhood right when I have a big agenda to get through and end up having to kill them all because they pissed me off. :)