Regarding the overflow- check out the durso stand pipe. It is propably the best DIY
for adding a sump/fuge to your non-drilled display tank.
I have a 40g main, and 30g sump/fuge - like 20g is actully devoted to the fuge. 3 inches of sugar aragonite, some hair algae, tons of pods
and copes, chems have been flawless for 3 months, even with a missed water change here and there.. just don't forget to top off
2 things I would have done different (this one I will change) - use a larger bulkhead fitting to allow for more h20 flow. create a larger sump area (maybe 50/50 on the 30g tall I used) reason being- if I miss a top off my pump sucks air in about 4 days.. I have to top off every 2-3 days..
if you have the time/$$ and space- go with the combo sump/fuge.. and a decent sized overflow if you don't have a drilled tank.
30g sump/fuge (low flow)
's and via aqua 2600 sump pump
on 3/4 plenum
3" sugar aragonite in fuge with hair algae
20w white NO
50/50 (2 bulbs)
20w actinit 2 damsels
h2o quality is solid 0's. 80 d.