Own Router and Modem

So how would this work if I got my own router and modem? ... how do i receive unlimited data.

Your question is not clear. What do you want to know about getting your "own router and modem"?

Regarding unlimited data, the fine print near the bottom of https://www.xfinity.com/learn/internet-service says:

... Unlimited data available to customers without an Xfinity Gateway for $30 per month. ...

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