You or a moderator should move this question to the vSAN sub-community.
"If those are no longer available or newer drives are available that are more desirable, it is okay to add different cache and capacity devices of the same size? What about larger?"
Provided the cache/capacity-tier devices being added or on the vSAN HCL this is supported.
Adding larger/smaller devices is fine but always aim to add devices of the same or greater performance capability , otherwise you potentially risk slowing down your cluster.
Aim to evenly distribute added space at the host and Disk-Group levels - e.g. don't just add 4x1TB to one Disk-Group on one node, add 1x1TB to each of all four nodes etc.