You may find Dragonspyre a little difficult at the level you're on. I suggest doing Grizzlehein and Wintertusk first to boost your level and for additional spells: one in Grizzleheim and the other in wintertusk, If you craft, there's crafted gear in Wintertusk
Do Grizzleheim at least up through Ravenscar. There's a spell you could have earned at level 35, but only as you progress through Mirkholm Keep. Then going the rest of the way through Ravenscar sets you up for Wintertusk.
Wintertusk is much harder than Dragonspyre, so difficult that I wouldn't recommend it unless you're at least level 48. Even then it will be a huge challenge, but in return you advance very rapidly.
If you decide to do Dragonspyre first, be sure to complete Wintertusk at some point soon afterwards, as many of your future spells and pets will hinge on you questing through to at least Nordriland.
have to be level 50 to do half of Grizzleheim . . . but Dragonspyre too hard at that level; what I did was start Grizzleheim until you get sent back to Merle then do Dragonspyre until Merle calls you to send you back to Grizzle; BUT, my wiz was 48 when I went to Dragonspyre, not 38.
I skipped a lot of side quests, you must have skipped a lot more cause you will have to run with friends to make it through DS
I have a fire that is level 38 and I recently finished Mooshu
What should I do next? continue with Dragonspyre and then grizzleheim or start Grizzleheim and then Dragonspyre?
I would recommend going as far as you can in Grizz then jump into DS. There are level requirements for a couple of areas in Grizz so when you get to those, go ahead and move into DS. You should get a message from Headmaster Ambrose when you are able to return to Grizz.
I prefer doing Dragonspyre first, and then do a little bit of Celestia before doing Grizzleheim. Grizzleheim will be really easy at that point where you can just fly through it. Then I'd recommend doing Wintertusk before returning to Celestia. Wintertusk, unlike Grizzleheim, provides a lot of XP. I find that the extra levels you gain during Wintertusk make a big difference while finishing Celestia.
Do Grizzleheim to get your level 35 spell and to boost your level up to lvl 42. Trust me, you're gonna need the extra power for Dragonspyre.
I also recommend doing Wintertusk after you finish Dragonspyre, so you don't have to wait so many levels to get your damage enchants in Celestia, and there are some decent ring and athame drops there as well.