So this is a long reply because we need more info, it’s temporarily a complicated subject, and because some of the solutions are untested by me.
First, why aren’t you able to use your old V1 cabinet sensor?
If it’s because you replaced the old Bridge V2 camera with a V3 cam, then consider running the V2 cam is a corner somewhere to continue to support the V1 Bridge and your V1 sensors.
If it’s because the bridge is bad, then you will need a new V2 Hub (to be discussed later), assuming your current V1 Bridge doesn’t work in another V2 camera.
If it’s because the V1 contact sensor you are using on your cabinet is bad, then if you don’t have another V1 contact sensor to repurpose to that duty, you will need a V2 entry sensor WITH the new Hub. The store will tell you that a V2 sensor will not work with a V1 Bridge.
Getting the V2 Hub:
The only way to get the new V2 hub today (what used to be called the bridge) is to buy a WHM package.
Hopefully soon they will sell at least the starter kit without WHM, or the V2 Hub on its own. But with production of the Hubs still limited, we aren’t there yet.
To answer your other questions:
ATM you have to at least buy the license. However, the license is $60, and they are giving you a $40 discount on the starter kit. So you are paying an extra $20 for what they send you.
I would expect the V2 Hub to cover the same distance as the V1 Bridge. That is to say, a small house (1500 sq ft?) If you need further, there are many techniques that can be applied, like putting the V2 Hub or V1 Bridge camera on an extended WiFi leash.
No. Just don’t activate the WHM license. If you DO activate the license, put it in Test Mode and leave it that way if you’re not interested in active monitoring.