that poor yellow tang. that tank is way too small for him.
that second link, the reef shop, has power heads made by Hydor, called Koralia.
These are ok for the money.
Hydor Koralia K3
that same website also carries "quiet one" pumps. one of these is what i would choose for a return from sump.
I would get that tank drilled in the back, instead of using a HOB
overflow box. a single hole about 4" from the top and 4" from the corner will do. I would drill it for a 1.5" bulkhead. that will be more than enough.
This would use gravity to change water, instead of siphon- a much more reliable set up.
i would have the return come over the top. no need to drill a second hole.