On the subject of drilling, my approach is to print an undersize hole, and then drill it using a larger drill to the required size, the small hole will guide the drill, I do mine without a drill press and they come out ok. To prevent melting do the drilling in short stabs, as this prevents any heat building up. Running the drill backwards at high speed smooths out the bore.
Smoothing PLA is something I have only just figured out on my SU76 build, get a surface horizontal and dab a brush well loaded with varnish onto the surface until it is covered, don't brush it. The varnish fills the ridges and smooths out the surface. They are still visible through the the varnish when it dries, but once the paint goes on, they disappear.
Great work on those suspension units, they are impressive!
