I learn and re-learn the common sense stuff:
1) Know and comfortable with CAD? You're way ahead of me. In my case, I need to stay on paper and cardboard for as long as possible. But if y ou can outsource panel cutting with a reliable CAD file, it would be a lot easier than my 8 iterations (paper, cardboard, thin plywood and then aluminum).
2) Aluminum is better for panels because of the design of the avionics mounts. 2024 is everywhere but bending 6061 is lot easier than 2024.
3) The project I acquired had the standard madness of a composite panel cut to spiderweb by all the instrument holes. A spiderweb cannot add strength or stiffness to the structure. Now a radio stack ties the panel to F28 (fore-aft stiffness) and a bit of square tube runs across the panel bottom, tying together the right and left fuselage side.
4) If I knew for certain what my layout would be, I might make it modular. But maybe not – most of the wiring is across the natural panels, and it's just as easy to pull displays as to pull a module.
5) I should have created a wiring channel before I wired anything other than the 4AWG power and ground cables. I clipped open the ugly bundles and am doing it over, threading wire through jumbo Adel clamps hanging on the bottom of F28. The upside is that I have yet another chance to test all my connections.

I worked the last wood template near to death - when I made mistakes I patched it with flox and tried again. I found and solved all my clearance issues and changed the layout multiple times. With the wood perfected I started working on aluminum sheet, first with .063 2024-T3 then .050 6061. See below on aluminum alloys. I worked through multiple colors before setting on flat black with labels of white text on black. Lesson - don't trust "paint and primer in one" over any existing finish and don't spray a clear over anything from another family. To secure the panel to the composite perimeter frame I like AN3 bolts and 10-32 machine screws into 2-lug nut plates, floxed to small pieces of G10 and topped with a layer of fiberglass tape. These suckers hold, and the compressive load is the aluminum sheet on one side and the G10 on the other.
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Side bar on aluminum alloys....The former panel was aluminum alloy 2024 - readily available and easy to cut and drill. Even so it is easier to work with the recommended alloy, 6061. After the rolling mill 6061 is a lumpy mix of magnesium, silicon, and other elements in aluminum. Solution heat treatment is done by raising the alloy temperature to about 980 degrees F and holding it there for about an hour. This dissolves all the alloying elements into a solid solution in the aluminum. Then quench the alloy in water - cool it rapidly enough to prevent the alloying elements from precipitating on cooling. at room temperature. This is called the T4 temper. If we take this material and heat treat it at a temperature between 325 and 400 degrees F, the alloying elements begin to form ordered arrays of atoms in the aluminum matrix. These arrays are called GP zones, and they strengthen the aluminum considerably. This is T6 temper and how I bought it. Heat it again, the ordered arrays break down and the sheet bends easily. Now the clock is running...an age hardening process takes place at room temperature over a time period of four to five days, with 90% of the hardening occurring within the first day. Because of this effect, aluminum parts often need to be shaped soon after a heat treatment process.

Here's the mechanics of annealing in the home shop. Mark the bend line, then use a candle to put light soot on that line. Think through the bending jig and handling hot sheet, _then_ use another heat source to burn off that soot line. I have a propane torch, and w/o an O2 feed it burns at 2000 F - I play the flame over the bend area to raise the temp gradually. The soot line burns off at 700F, and then I use a spray bottle to quench. I clamp along the bend line and the annealed 6061 bends with hand pressure. To get a crisper bend I use wood blocks and soft hammers. It aircools over 5 days, and is reported at 90% strength within 24 hours. I understand this is a T5 condition, not T6, but has the rigidity I want.
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For layout I repeatedly used the Cozy template in X-Panel software, muttering all the while. I do not recommend X-Panel - expensive and the ability to export a CNC file is even more expensive. The template doesn't fit this airplane. The outline view is _not_ a cutting guide - it will show the instrument's total dimensions but not the panel hole.

Below is a template I found useful for my steam guages. Print it (use the "original size" option, paste it on a bit of aluminum sheet, market the center and corners, and outer edges of the standard instrument. Save it forever!