Looking good old chap. I normally paint the road wheels, and especially the tyres, before assembly - it makes access easier later, depending on the set up of course. On, say, a Panther, these can be done at any time before fitting, which is usually as late in the build as possible. With the Sherman's VVSS bogies, then it's easier to paint the wheels, and the bogie assemblies, then assemble the wheels / bogies.