Process of switching from AT&T

Hi I am looking into switching to xfinity mobile as it looks like it could be the better budget option for a family that doesn't use a lot of data. I have a couple of clarifying questions.

- For the 10gb shared pool, it's advertised as 60$ and from my understanding you could hypothetically connect 4 phones to the data pool and it would still be only 60$. Is that correct?

- If the phone number I'd like to move from AT&T is an out of state number from where I am living does that change my ability to keep it when I switch to xfinity? 

          Example: I now live in Massachusetts but I have a phone number from New Hampshire with AT&T, will I be able to keep the New Hampshire number?

- If I wanted to check the connectivity in my area before switching to xfinity mobile, is there some kind of sim card test kit available? 

- With all the fees how much would a 10gb shared pool between 4 phones actually cost on the bill (Massachusetts is the state)

- Finally, if I were to switch to xfinity mobile, would I get a discount because I already use them as an internet provider.