Small ISP Need to Know

[notcommonmistakes at gmail.com (not common)]

Hello,

I work for an ISP (35K customers) and do System Admin work for operations
and development (DNS, Radius and such).

I want learn more on our IP side (Routing, BGP, MPLS, Core Network).

I am trying to learn the Net Ops world piece by piece, and this is where I
ask:

Where is a good place (or places) to start learning ISP operations "Need To
Know"?

Thanks for your time