cannister filters dont run so well connected like that and are difficult to prime when connected like that, perhaps use it in a closed-loop system if you want to use it and it can double as your tank circulation(if you dont know what i mean by closed-loop google it ) then buy a cheap pump with a ceramic shaft for your return pump. What type of cannister filter do you plan on using? reason i ask is a large one say a cf 1200 you would likely fit all the chemical media in one tray and have a mostly empty filter as you wont need two trays of carbon in a filter that big for a tank that small
for your heaters i would buy two 50w heater and run both in the sump , there is a tiny 50w heater made by elite so you wont have any difficult fitting two and a return in , like you would with a single 100w heater
depending on how much live rock you plan to have in the display you could possibly leave out the live rock rubble in the sump and as for your lighting in there , i find some form of lighting helps to see what your doing etc but reverse lighting would only be necessary if you were running the middle section as a refugium and growing macro algae(seaweed) to help with nutrient export, however its my thinking than in a 30l sump(and i may be wrong ) you arent going to be able to have enough macro algae to have any noticable effect on nitrates or phosphates in my opinion you are better off having a skimmer section then a bubble trap as a divider and the second half as heaters/return will also give you more room to work with trust me you dont want no room when you are playing round with a skimmer