Hi Joerg,
If you want full redundancy, it is good to have L2 switches between the CSSs and the routers. This in order to avoid having a single point of failure on the crossover cables between the CSSs and the routers.
Also, don't use the physical interfaces of the routers as the DG of the CSSs, the VRRP address should be the DG of the CSSs. The reason for this is that if you use the physical address as DG, the CSS pointing to this router would lose connectivity if this router fails, so it is better to use the floating IP as DG.
Besides that, I see you have a good picture of what you needs to be done to get this working. Thanks!
Regards,
Jose.