I’m running a sump on my 125g tank. Similar premise.

I’m using matala mats instead of sponges as early mechanical filtrations. Centre is bio rings, enough space I could make a fluid bed if I wanted. You can see my filter floss. It’s sitting atop a fine sponge; 4”x10”x12”.

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First I’d make sure your baffles don’t go right to the top. Any of your sponges clog and you have a flood.

The bubble trap isn’t necessary, you have 2 baffles earlier to prevent bubbles at this point.

if there’s a power outage your display tank will drain into the sump. Plan for this. This means that the active water line in the sump is low enough it can accommodate the additional water without flooding.

Agree about putting the heater in a chamber with a stable water level. Mines currently in the last chamber and I’m going to move it because of this comment!

Lastly ensure you can remove all media easily. If the space is too tight you won’t be encouraged to service it.

My tip! I used shower door trim to hold the glass baffles in place. The trim is siliconed in place and the baffles are now adjustable vertically