Let me be sure of your plan:
So, you plan to create a side account and make it your new main so you can get the free NC that comes with creating a new account, then you want to make it your new main account until you get a gift box and send the cookie you bought with the free NC to your old main/now side account? And repeat that with all the sides you're allowed to create?
Even though creating a new account collecting the NC and making it your new main isn't a problem I think doing this a few times in a relative short succession might raise suspicion and is really borderline. Especially if you will be donating the money you get to the tree. They might think you're playing on multiple accounts. Switching main accounts should be done max once a year to be safe.
Creating multiple accounts just to get the free NC and transfer cookies to 1 account this way might be considered cheating and I would NOT recommend it. Better would be to buy mystery box capsules on your main and use those to get items/cookies bought from the free NC on your side back to your main.
OR even better: you can just complete faerie quests on your side account and if you want to give the stats to the same pet you could just transfer the pet to that account. Just make sure that all the items, or NP to buy the items, needed to complete the quests come from your main account.