when I was on lvl 55 i did all of the grizzleheim quests (even side quests) and then i did the last quest in mooshu to get me in dragonspyre on lvl 60, now im on lvl 66 and im starting celestia is that good or bad?
Being a higher level will definitely help you and allow you to battle and complete quests with ease. In my experience, it seems like avoiding the side quests will allow you to even out experience-wise with your fellow quest buddies, as it will be more difficult for you to level up than them due to your higher level and need for more experience.
So, as for the advantages of your situation: -You'll be able to solo bosses -You'll quickly complete quests -You won't have to worry about health as much as the players around you
However, the disadvantages: -You will struggle to level up -Your fellow players will quickly catch up in level to you -Gear earned in the area won't be as good as say in Zafaria or Avalon.
Your level is fine. Being so advanced may make Celestia seem very easy for you. That could be disappointing if you like a challenge, or it might make the world go by really fast if you enjoy speed. Gradually, the worlds will become more difficult as you level up through them and you can look forward to challenging times ahead.
It's actually good that you finished all of Wintertusk, because doing that means you'll have no trouble receiving all of your pet and spell quests later on in Avalon and beyond. Some of them require you to have your level 35 & 55 spells that you earned from Erik Wyrdruin and your level 58 pet that you picked up in Nordriland.
It's not a goo thing or a bad thing. It's jut a thing that means you'll now be able to do darkmoor allot faster then your questing buddies. And get better spells before them if that's what you want.
when I was on lvl 55 i did all of the grizzleheim quests (even side quests) and then i did the last quest in mooshu to get me in dragonspyre on lvl 60, now im on lvl 66 and im starting celestia is that good or bad?
You're high level for starting Celestia but that's normal for anyone who likes to complete all the side quests. It has pros and cons, only you can decide whether it is good or bad.
One of the requirements to going to Celestia is that you must be at least level 44. You're a lot higher level than that but the concept of being 'over-levelled' is a matter of opinion and very much depends on how you feel. Balancing what level suits you (minimum - average - high) depends on what you enjoy most!
It can be really fun to be stronger, have higher health and be able to manage the battles with ease. Defeat and Collect quests or mob battles are much quicker and you can face bosses or tricky dungeons even when you don't have friends online. Doing all the side quests is fun too and the sense of completion can be satisfying. You won't miss any secret quests that result in cool rewards or exciting challenges. You also open up everywhere to be able to help others, explore and go back to for reagents, drops etc any time you like.
It can be a little frustrating to be unable to go somewhere for a pet or spell quest even though you're at the 'right level' or get a daily assignment sending you to an area you haven't yet unlocked. If questing feels 'too easy' and you're not enjoying it as much then you could stick to main quests for a while and only do the sides that give spells or pets etc.
Honestly, I don't think level matters if you are having fun! If I am struggling I will do more sides to level more; if it's getting too easy I stop the sides for a while to even up the difference. I'd rather be higher level than required for the content than lower level and struggling.
You are high level for starting Celestia but gauge whether it is good or bad by how fun it is. If needed, adjust which quests you do if it could be even 'more fun' closer to the average level