Hey,
With resect to Hardware understanding of MX devices, https://www.juniper.net/documentation/en_US/release-independent/junos/information-products/pathway-pages/mx-series/mx960/index.pdf ,this has a very detailed explanation and I think is perfect.
However, to understand the architecture of the device, infact the entire MX series, the best read would be the MX series by publisher O'Reilly is perfect. Its worth it.
https://learning.oreilly.com/library/view/juniper-mx-series/9781449358143/
Hope this helps to start with. Youtube has a lot of stuff too. And this KB for Cisco to Juniper migration.
https://kb.juniper.net/InfoCenter/index?page=content&id=KB15482
Thanks,
Pradeep
Please Mark My Solution Accepted if it Helped, Kudos are Appreciated too!!!