>>8062864The crabbo will do. It has at least one unofficial build (this weird dragon-esque thing) and a lot of room for partswapping (tons of pegholes, tons of legs, and there are quite a few spare parts left over after you're done building to play around with).
If you can manage it, I would also buy one or two MSG weapons sets that look like they have a lot of modularity, those tend to mix well with Hexa Gear.