Old school time honored drill and hand tools works. Lay out pattern. Use spring loaded center punch to drill 1/8" to 3/16" holes inside your pattern. Space the holes (2) diameters apart (leaving 1 Dia material or less between holes) and half hole Dia. + 0.032 inside your trim line. The holes will be near but not over the trim line. The center punch locations must be precisely located. If that is done properly the rest is drilling, cutting and filing.
Open up a few holes in a row and use a hacksaw blade with a handle and by hand connect the dots (cut tabs between holes). Use a hand file to smooth the edge. If done carefully it result in a good cutout with minimum dust. Power tools rotary files and cutting wheels will spew aluminum dust. Drilling holes produces chips but they don't go flying all over. Hand hacksaw and filing creates dust but it tends to fall straight down not fly all directions. You can mix this with drilling holes and powered cutoff wheel to cut the tabs between holes, if you are skilled it. Be careful in the corners; you want a small radius not a sharp notch.
If you go powered tool route, tape the area off really well to keep dust getting into avionics, switches, connectors. If you lay out the holes carefully with your center punch, drill straight and cut out the tabs between holes you will have an accurate cutout.
This is old school but it has been done for a long time and works and still works. Free hand cutoff wheels works, if you have a steady hand and is faster. However fast and a big Doah!, is not time saved.