First of all, a sump is not a replacement for a cannister filter. A sump is a place to increase water volume, hide equipment (heaters, protein skimmers, thermometers, etc.).
Sumps can also house some GAC
(carbon), poly filters, other chemical bags (ChemiPure) etc.
in quantities of 1 - 2 pounds per gallon of tank volume give you the surface area to house the beneficial bacteria that would normally be in the cannister fiter. Unlike the cannister filter, you will not lose these bacteria when cleaning the filter.
For NitrAte export you need to add some macro alage, a/o do PWCs religiously. PWC
's will keep nitrates in check even with a cannister filter.
You can get a hang on PS too.
Your tank right now is a FOWLR
. You say reef, so tell us what you plan to add in the way of corals and what lighting you currently have.
I would reccomend that you give yourself and yoru tank at least 6 months to mature before adding any corals. The tank needs to mature and you need to learn how to care for the tank and the inhabitants.
Keep reading the threads and the articles on the forum.
As for your sump build, Eshopps also makes overflow boxes. You will need one of those to get the water from the tank to the sump, and a pump sized to the overflow to return the water to the tank. Read the SUMPS article on this site. It may explain alot.