One needs to walk a thin line (literally!) when it comes to bases for 1/600 scale figures. Too thin and you can't pick up the base: too thick and the base ends up distracting your eye from the figures. I find that a thickness of 1/32nd of an inch (roughly .75mm) is just perfect, though thicknesses of up to 1mm are fine. Beyond 1mm, however, and you run the risk of having your figures look like they're standing on platforms.
Because of the smallness of the scale, I try to make stand types immediately apprehendable to the eye. I use 25x25mm for armored targets, 25x15mm for unarmored targets and round 25mm for headquarters. FAO and FAA stands are mounted on equilateral triangles, 25mm to a side. Recon units are based on 25x25mm stands with an angled front edge. Finally, COs are based on 30mm round stands. The first three stand types I buy from Litko in 1/32nd inch thick transparent acrylic with rounded corners. The next three types of bases I cut myself from plasticard or artists' matte board (I use a fingernail clippers to trim the corners to Litko's standard.
There are two basing methods: one for freestanding vehicles and the other for units which come with a pr-molded base (generally infantry and guns). Both start, however, with basic cleanup and separation of the figures.
O8 uses some ultra hard and fairly brittle alloy in its figs. If I didn't know better, I'd even say it was aluminium. It has ZERO give, so you can't correct (the thankfully almost uneard of) casting errors by bending the metal back into place. If you try, the metal will snap. The strength of this allow is enormous, however, and it takes alot to get it to break, which brings up another problem: the tiny bits of flash on the figs can easily pierce your skin like little needles if you grasp the wrong.
I use a fingernail clippers or a small wire cutters to clean the flash off of my figs. First I clean the helmets of any spurs (they generally have some because that's where O8 likes to put some of its flow vents), then I snap off the big bits of flash. Finally, I break off any stands mounted in strips. To do this, I wrap the strip in cloth and simply snap it along the molded separation lines. The cloth is necessary to avoid mauling your fingers - as I said, this metal is strong stuff!
Fingernail clipper for cleaning up a 25lb gun. Note the molded separation line between the lorried and unlorried gun. Enough pressure will snap that cleanly in two, but make sure you protect your fingers while applying pressure!
I generally put down two vehicles per stand as I feel that this gives an acceptable feeling of mass without makiung things look too crowded. Even so, you can see in the pictures below that my Grants are pushing it. I should've moved these farther out to the base edges. Oh, well...
Applying the first coat of paint
The 201st Motorized Brigade. HQ up front, followed by carrier companies, infantry, machineguns, 2 lber ATG portees and mortars. Mortars should have been based distinctively from MGs, so I'm going to have to visually define them better come painting and flocking time.