Don't take it personally or negatively, the forum is a collection of peoples thoughts and inputs and my comments are meant to help. As I said, it was only my opinion that you are highly stocked.
There is no reason for any of them not to make it to full size.
I think you are well on the way to the solution and do not forget that you simply need a large surface area for bacteria, how you do it is up to you and there is not a wrong answer.
You can improve the filter by adding some airstones in the bottom to help feed the bactria with oxygen and agitate the media, this could signicantly reduce the area needed as long as reliable.
I would then focus my attention on making large water changes simple to do as these will be the life blood of the system, if you make them easy then it takes the ball ache out of the job thus making them more regular and less likely to slip. (i.e. tap inlet or auto real hose near the tank and an easy route to waste)
There is no reason for any of them not to make it to full size.
I think you are well on the way to the solution and do not forget that you simply need a large surface area for bacteria, how you do it is up to you and there is not a wrong answer.
You can improve the filter by adding some airstones in the bottom to help feed the bactria with oxygen and agitate the media, this could signicantly reduce the area needed as long as reliable.
I would then focus my attention on making large water changes simple to do as these will be the life blood of the system, if you make them easy then it takes the ball ache out of the job thus making them more regular and less likely to slip. (i.e. tap inlet or auto real hose near the tank and an easy route to waste)