filter for 120gallon planted discus

i currently have a atman df-1300 ( 1500 L / hr )
what is a good filter to add on with the current filter ? was thinking of the model jebao ( 1200 L / hr ) .

also , my new tank will be coming next week.

is it alright if I

1: move 4 discus in a pail
2: drain the tank water
3: transfer the current ADA new amazonia to the new tank + 2 packet of ADA new amazonia
4: add in water to the new tank
5: transfer old filter to new tank + new filter
6: move the fish in

??
since the filter have already been running for 1 over years and the BB has set up its colony.