My comment about flow being a consideration goes towards the length of the weir you're needing plus the size box to be built to handle the bulkhead you'll use. My point being on a small tank there's smaller panels of glass to cut into.
This RC
calculator give length of linear weir for flow (though it doesn't give height of water about) plus bulkhead.
The overflow calculator download (Excel spreadsheet) in this
link can give an idea of size needed if using a slotted weir.
Maybe something to consider was Fish's approach on his
pico visible in the first video maybe not a overflow in a true sense but wasn't obtrusive.