That's a decent setup. I have 5 of the slim, XL OCD tanks, with Smoktek 3.0 ohm single coil cartos running on a Provari. These are really nice pyrex tanks, and the price can not be beat.
4-5 days on one carto in a tank seems about right. As you begin to collect more tanks, you'll note a little longer time with each carto as they are sharing vape time with the other tanks. Less time with the darker colored and vg-heavy juices.
I always recommend to cartotank users, new and experienced, to pick up the tank tool known as the Slap-yo-Momma from Big Daddy Vapor. It does 2 major things. It protects your tank's rubber o-rings from the sharp edges of the carto end when it is passed through the endcaps. It also greatly aids in the speed with which you fill/refill your tank with juice by blocking the juice from getting into the carto air hole. It is without doubt the best thing I have bought since I've begun vaping....besides the Provari.