I havent planned out the sump quite yet... still debating on buying a 37g to convert, or acrylic to build.
Though, I'm probably doing something similar to this: Bogopolis - 30g w/ 20g sump (Pic Heavy)
where it is primarily mechanical w/ an area in the center for additional fish, or shrimp, snails, and maybe even emerged plants to allow their roots to filter the water.
with a planted tank, I don't see a huge need for a bacterial filtration "department" when you've got a ton of surface area with bacteria growing on them in the form of the plants themselves.
Though, to be fair, I do use canisters on my smaller tanks, and may set one up with stuffing for really getting the water crystal clear.