Best to start a new thread Nel
But a few quick answers for you
Take all the sponges out and all the media balls out these just act as a nitrate farm
Slap your skimmer in the furthest right compartment as you look at the front
Heater in the 2nd from the right as you look at it
UV and return pump in far right
Empty compartment can be used with broken up LR or better still stick a sumbersible LED in there and a bag of chaeto for Nitrate exchange.
Why do you need an LED in with the Chaeto? Is it to give it enough light to grow?
Thanks