I am doing only main quests right now and I am level 46 in Celestia. So far I am not struggling too much but I did just enter, should I do side quests or just main quests? Will I be the required level 55 for Celestia if I continue on this "main quest path"? PLEASE HELP!
To be honest, being at only level 46 and already in Celestia sounds like you're gonna be in for a, well rather unpleasant awakening as you've to understand that even though the world's difficulty was nurfed, it's still not to be underestimated. If you intend on soloing for the most part, I highly suggest you do the side quest along with the main ones. The sides are there for a reason, the experience each quest gives adds up and hence gives you a fighting chance against the various mobs throughout the world.
I am doing only main quests right now and I am level 46 in Celestia. So far I am not struggling too much but I did just enter, should I do side quests or just main quests? Will I be the required level 55 for Celestia if I continue on this "main quest path"? PLEASE HELP!
You are already in Celestia so you don't need worry about the required level for getting into the world. If you mean Zafaria then I am pretty sure you will level up enough to get there after Celestia ends. Wait until you beat Celestia if you are main line questing and if you didn't level up enough then you should do side quests.
I think you are fine to continue main quest. If you decide that's not for you or you get sick of Celestial then you can go back to GH. However I'd stick to the main quest.