Best to do your shopping in Milan - at least for what you were looking for. Start around the high end stores in Galleria at the Duomo area then make your way down to the NE side of the church. Lots of retail stores there, both high and low end.

I would just enjoy Venice. Select a good tour book here before you go, ie. Frommers, etc and scan the restaurants section as they rate them according to price and sometimes quality.

have fun.