It's totally fine to make as many as you want if you stick to the traits available to you (thank you for joining btw), since you have joined, the entire Uncommon tier is at you disposal as well as 2 Rare traits for each Shellpup you create~! You may earn an extra Rare trait for ONE Shellpup if you advertise the group somehow and prove that you have done so! Otherwise, if you would like more Rare or any Mythical traits, they can be purchased but they only apply for ONE Shellpup~!
If you create your own, please submit it to the "Shellpups Approval Centre" gallery so that we may approve your design as an official Shellpup and any art of approved Shellpups can be submitted to the "Shellpup Art" gallery. For a list of trats, either go into the "Shellpups Info and Guidelines" gallery and read through the journal or go on the "About Us" page to see only the traits
I hope this helped and if you have any more questions, please let ne know ^^