For your overflow if you want quiet, might consider a Herbie style. Only being able to drill on the backwall still could be done like
Reefjunkies with an internal overflow chamber or with a external chamber where you would need notch out the backwall (such as
Skimmin's old tank)
If not the Herbie can still do a Coast to Coast chamber style (
a complicated example) or even something just from a
horizontal piece of PVC.