Would it be considered against site rules to buy my own designed Custom Wearables for someone? Is it allowed for the artist/creator to purchase their own creation? Or to gift their own copy?
No, it's fine to buy your own CWs and then do whatever you want with them :)
For future reference, questions relating to the rules are typically better answered by filing a ticket but this has always been allowed - you're not obligated to sell your item(s) to others or to limit yourself to one copy :)