Congrats on the new tank! I have a YWG in the 13.5 EVO (paired with a Randall’s Pistol Shrimp). I don’t think it’s too big for this tank at all. I have a tailspot blenny and a pair of orange storm clowns as tank mates. It’s arguably overstocked with those 4, but it’s peaceful and I am diligent with maintenance.
I’m not far from you (Boston) and there’s a good chance the LFS you’re talking about might be where I got my clown pair and YWG (Blue Light Aqua). If it is, you’re lucky to have Myk so close. He quarantines all his livestock and buys his clowns direct from Sea and Reef in Maine which is among the best aquaculture facilities there is. He’ll custom order too if you ask. He’s the only place relatively local to Boston that I’ll buy fish.
*edited to add
* If your budget is tight, check out the 3DOcean media baskets. I had the InTank basket and ended up switching to this one. It’s cheaper, and it seems to do a better job of directing flow over the filter media.