I already have a CSP and I plan on opening the CSR, should I keep both?
Probably not considering there is nothing the CSP can do that the CSR can't. As always, it's better to downgrade to another card than cancel outright (e.g. downgrade to Freedom, and yes you can have multiple Freedom cards).
Does the 1.5cpp only apply to points earned on the CSR?
No, you can get the 1.5cpp in the Chase UR portal from all your UR points by transferring points from your other UR-earning cards to your CSR.
This means the Freedom Unlimited effectively earns 2.25% and the Freedom quarterly categories earn 7.5% if you also hold a CSR and spend your points in the UR portal.
Source:
https://www.reddit.com/r/churning/wiki/chase_sapphire_reserve