if you use spikes for stability purposes only, then use something lighter such as extenders or skirts. it frees up more weight.
weapons are only to be used for actually doing damage, or for aesthetic purposes in IRL. using weapons as stabilizers is a waste of weight, and everything in RA2 building revolves around proper weight management.
and 5mm alu by itself is fine, but since armor choice is really something that multiplies your empty chassis weight, better make a smaller chassis.
I would put the motor outside as well.
