Plasma arc has a "sweet spot" in thickness when it comes to cutting materials and thicknesses. The faster a material conducts heat, the worse job plasma will do up to the point of being useless. This is largely because the hotter the material, the faster the torch travel must be for satisfactory cutting. When the temperature of the material is in constant flux, it is next to impossible to set a cutting speed that isn't either too fast or too slow. This is not to mention the warpage issue.
Heat travels much faster in sheetmetal than in, say, 11 gauge and above. So much the worse in aluminum sheet. On the other hand, when the material gets over maybe 3/8" thick, the bevel in the cut face becomes a consideration.
My suggestion would be to farm out shape cutting in sheetmetal to a laser cutting service such as
sendcutsend. Shear the straight cuts.