The next step would be to create the Baffle Walls.
In a Berlin Style sump, this consists of 3 walls. Two of which are identical.
The first thing you'll need to do is to measure the width of the tank in the ID (Inside Dimension). This needs to be as precise as possible. Scribe this number down because it will be the width of your baffle wall. I actually decreased the number by a 1/16th of an inch for ease of placement but the closer you can get to the actual dimensions the easier it will be to secure them with sealant. These aren't a structural joint. You're just trying to seal the edges so the water has to go through the ports you will cut.
The second step on the baffle walls will be to measure the dimensions and mark them on the acrylic sheets with a Sharpie. Accomplish this by measuring with a tape measure on both ends and then use the ruler or straight edge to scribe the line. This is easier by clamping the ruler to the acrylic sheet and your piece of plywood.
The next step is the water ports. The two identical walls are the ones closer to the ends. These walls will help establish the height of water levels and there lack of turbulence. The middle wall is between the skimmer chamber and the return utility pump. See Images below for what they should look like. The quantities I have below are for (2) Sump tanks. If you are creating just one Sump the quantity will be half of what I have below.
Once all the cut lines have been marked you can proceed to the next step. Note: The width of your Baffle Walls is depicted by the ID of your Sump Tank