newbie piping questions - what size return - what size overflow?

[golf nut]

Stick with the first plan aq-rear-1.jpg unless you are prepared to drill more holes, if the holes are drilled for 1 1/2 bulkheads and you use a nominal return pump then the Herbie drain will be more than adequate, if they are only 1 1/2 holes in the glass then I would get it drilled properly in which case you have a clean slate to do as you wish.