i dont know much about sumps, was hoping for some help as well, i was thinking that would go in the 2nd compartment where the criss-crossed thing is, thats there to hold it up
I am in the middle of designing my new sump also. With my current sump tank water dumps on top of a filter pad in the drip tray over the bioballs which is working very nicely. I am strongly considering adding a compartment in front of the bio ball compartment to hold filter socks in my new sump and getting rid of the filter pad.
In your sump design the majority of the biomedia is submerged. The thing I like most about my current sump is the amount of O2 exchange I get from trickling water over bioballs. If you go with submerged biomedia like ceramic rings I would add air stones underneath the media.
If the plants are strictly for filtering (and they do a very good job at that) I would forget about aqueous plants and use terrestrial plants like Pothos (but this is just my strong personal preference).