i gather that you dont have an airbrush. so basically the best way to lay on paint would be with a large soft brush, and thin your paint a little so that you dont get brushmarks. for detail painting use a small brush.
as for putty, if walmart has any hobby putty, just get that, failing which, there is this stuff called porc-a-filler i heard of, available at home depot and the like. i havent used it or seen it, but give it a try. perhaps other people can tell you more about porc-a-filler. its actually for filling gaps in pottery.