If you choose a MiFi device you will not need a separate router like the Cradlepoint and without that type device you can't do WiFi as WAN either.
The answer to your question is that you have the pricing right, there are some additional taxes but not a lot and the biggest pitfall is using too much data. If you exceed your data limit you will be charged for that overage. It's $15/GB when you go over unless you change your data plan before the month ends and then you can add 2GB for $10 (check your plan to verify).