Drive capacity and cloning...
You're fine with regard to the disk space. You'd have a problem only if the original drive's used space was larger than the capacity of the new drive. The partition will resize to the max available on the new drive during the cloning process. The used space might appear larger on the old drive because of file fragmentation.
Firmware update...
You should always update a drive's firmware first when possible. The good thing is you have the original disk and it's intact. Any SSD's firmware update tool always has a disclaimer regarding data loss, but the worst case scenario is you update the SSD's firmware, you have data loss and just re-clone the drive. That being said, in most cases, the firmware update will go without a hitch.