Nice tank just looked it up. I've just started a 10g fusion myself.
RE filter chamber, something like this.
https://www.fishpond.co.uk/9999219018495?utm_source=googleps&utm_medium=ps&utm_campaign=UK but for USA obviously. Sorry I'm across the pond.
Carbon and floss etc can be added to Chambers. Really good.
The pump, yes can upgrade ether but I'd look in to how many gph the weir will take first before spending. If its not much more than night not be worth changing it.
Fluval do skimmers for that tank so could look into one of their own. Tunze do compact skimmers which are good.
I went for ghost skimmer on mine. Not the best but does what I need it to.
Other option is to go skimmerless or maybe use a miracle mud based system.