The Protank is the clearomizer (liquid tank and coil) that will sit on top of the MVP2 that you get.
I recommend that you get a back-up system in case your MVP gets dropped and dies. That "spare" may work for your wife. Also, I have multiple tanks so I can switch flavors without cleaning so much. I usually have 3-4 tanks with juice going at any one time. Until you settle in, I would stick to Protank 2s or all Nautilus tanks. The coils are different on many Clearomizers, so if you use the same clearomizer, you only have to buy one kind of coil to put in your clearomizers.
I recommend that you get a back-up system in case your MVP gets dropped and dies. That "spare" may work for your wife. Also, I have multiple tanks so I can switch flavors without cleaning so much. I usually have 3-4 tanks with juice going at any one time. Until you settle in, I would stick to Protank 2s or all Nautilus tanks. The coils are different on many Clearomizers, so if you use the same clearomizer, you only have to buy one kind of coil to put in your clearomizers.