To be honest, you'd probably find a very similar parts list for the 12lb-ers to the one posted above, just the same as a featherweight but with less armour. Of course, you could find smaller motors or go brushless in the future if you wanted to do so but for a first build I'd keep it simple and go for a pushy brick type one with maybe a lifter or an axe if you wanted an active weapon.

Dragoncon's table top events seem excellent too for newcomers, on account of them being geared more to being a 'show' rather than full on combat, so you'll be able to get plenty of practice in before going up against any of those nasty spinners.

What sort of tooling do you have, or have access to? That will probably be integral to what materials you end up using!