Welcome to the forum
First off there are a couple of things here that need looking at.
You dont want to have the media totally submerged in water, wet/dry being just that, some of the media is underwater, some above water. Can you explain the purpose of the lave rock? Is this for extra media surface.
Instead of having the lava rock in the first chamber, the pot scrubbers would be better there. Make a tower with a piece of foam on the very top before the rain tray, this way, you can filter the water coming from the overflow before it touches the media.
In terms of the height of the baffles, you need to not set them too low that water will just cascade over them, you want gentle water movement in the sump, not a raging torrent.
I would add the lava rock to the middle chamber. You can use ceramic media as well on the very bottom of the first chamber. Bubble traps are not really a necessity as much in freshwater as they are in saltwater.
I would also consider putting the heaters in the second chamber and not right by the return pump, if you ever get a situation the overflow fails, having them in the return chamber potentially opens them to get dry and explode. If they are in the second chamber, not only does it give more time to heat the water before going back to the main tank, it allows a safety margin, as the return pump will empty most of the return chamber before the middle one, allowing the heaters to still be in water, should the overflow fail.
Welcome back to the hobby and hope you can find some useful information here from our members.