custom figure sequence

so, when I finish the sculpt and after sand it , still need to use the dish soap to clean it ?

I assume you would want to wash it anyway, unless you want a bunch of dust in the paint

You wash a figure with soap to remove any grease from the plastic.

You sand surfaces with fine sandpaper to get rid of any slick surface, to let paint and clay stick to it better.

You sand hardened apoxie/clay when you have to. I mean, if the surface is all lumpy and crap, go ahead and sand it smooth so it looks better lol.

ok, basically the first thing you want to do is clean your figure with soap and water, then sand all areas you intend to paint or add sculpt to so it will adhere better. After those steps are complete you can add your sculpt (which you can sand to smooth it out, but that's optional and entirely up to you), then paint the figure. Super glue on the joints is also optional if you've done a GOOD job of sanding/filing/dremeling them down to avoid rubbing, it will add an additional layer of protection, BUT if the prep work is inadequate super glue will NOT prevent paint from chipping/flaking off from the joints, so keep that in mind. After all that you can finish off your work with a sealer or clear coat. Hope that helps.