You shouldnt have to drill anything. Just request it when purchasing. Tell tjem to order you a 180 dual/single overlflow with x size bulkheads. Sump can be a used 55 gal or smaller. Thsts the thing with sumps you can do basically anything you want in them, want a reactor throw it in the sump, spare bio, heaters, what ever u can think of just throw it in the sump. Holds way more bio than cans and if you go with filter socks maintenance is a breeze no squeezing out foam pads.
While your planning the poly stock you should research sumps and plumbing drainage methods.
Start a thread in the filtration section those guys will have you up to speed in npo time. Way too many options (bean animal, herbies ) to discuss here. Im serious i wouldnt have gotten a large tank if i wasnt able to put a sump on it.