Is your main goal milling only aluminum? What kind of parts? what size foot print, If you make the machine smaller than the recommended size aluminum will not be an issue. I cut aluminum fine at 25x30x2. Smaller and I could go much faster. New parts are on the horizon that will also make it more rigid.
If you have a specific need I can help a little better but as it is I am doing pretty good with aluminum.
The one answer I can give you is we are not lacking in power. Other machines use NEMA 23’s because they only have 1 stepper per axis, not an issue here. Matter of fact we aren’t even running these steppers at full power.