At first, while learning the phone, you're gonna use a lot of bandwidth, especially if you use Siri. But if all you're been doing is e-mail and EO, then clearly the bandwidth mountains of EO ads are to blame.
The Aircard is $50 now. Hasn't been $60 for quite some time. The 5 GB data plan on the phone is the same.
If you use the phone as a hotspot for the laptop, you really need to have the phone physically tethered to the laptop so the laptop can charge the phone at the same time.
I max out the Aircard every month, and either max out or come close to maxing out the phone's data plan (if it were 5 GB, that is, but mine is still unlimited). If you go with the 5 GB phone plan, you'll then have 10 GBs to play with every month. It's surprising how often I use 12-13 GB each month, 5 on the Aircard and then the rest on the phone.
My Cycle Date is the 4th, so I get a fresh 5GB on the 5th at midnight. Right now, on Jan 30, I'm at 5.633 GB on the phone and 4.254 GB on the Aircard.