Remember, R2 belongs to the ISP, so I think to add a default route pointing out to R1 is not a good idea...

R2 needs to have routes back your networks (which should be static routes.)  

I recommend you to use trunk mode instead of access mode on the ports between the router and the 5Ks. Also, always start with the 'switchport' command in order to be 100% sure that the port will work on layer 2.