Here is a link to an old thread of mine from when I was building my sump, it includes a link to the design I used.
The only issue I see is cost since your tank in probably not drilled. Overflow boxes can run $100 for a good one. Suggest you look at a 10g vs. a 5g. The more water volume the better.
A 10g will also give you more room for skimmer heater etc.
Besides a 10g tank is probably no more castly that a 5g is not cheaper.
If you are looking for a pure fuge I have seen the CPR style HOB
fuges that come with pumps and lights. They are very costly IMO