I don’t know about which Vitamix you should buy (I personally have a K-Tec), but I would definitely recommend getting a nut milk maker. I have a Soyabella by Tribest, and it is one wonderful machine to have. No blending or straining involved, just fresh nut milk whenever I want it. It’s quite a machine.
I have a turboblednd 4500 and it’s great. but the vita-prep is much more powerful. You don’t need a nut milk bag, you can make nut milks with your vita-mix. You may have to strain after blending depending n which nut milk your making.