Tank has a 2 gallon ATO chamber. I was looking at the Tunze 3155The best advice I could give is form a plan and stick with it.
I prefer skimmer over fuge.
Some run no skimmer.
My sump has no baffles.
I run a filter sock, skimmer, and a carx.
For water level you will need an ato pump and container.
You control your sumps water level with it.
Check out some build threads of tanks you like for more info.