Yes, several things to mention as precursors.. these sometimes get more actively discussed in our hardware&diy section, although you'll probably get some discussion here too. I think its always good to have an open mind about the 4 major manufacturers who compete in the external cannister area: Eheim, Fluval, Rena and Tetratec/(whatever the US name is, I forget, starts with an M) They all have plusses and minuses and if you do searches (eg. "best external cannister" and all sorts of other strings) in the hardware section there will be old discussions that have lots of pertinent info.
Another major decision is whether to go for one giant machine or two really big machines. There are plenty of obvious advantages to two filters (alternate maintenance days, redundancy) and there are more subtle considerations like the very largest filtration units sometimes coming with a big increase in noise.
~~waterdrop~~