Are different partition sizes OK?

I’ve outgrown my Bootcamp partition, so my current plan is to

a) backup my 20 GB Bootcamp partition with WinClone7,
b) delete the Bootcamp partition from an iMac Pro SSD drive,
c) create a 200 GB Bootcamp partition using DiskUtility,
d) restore my backup to the larger partition.

Does this sound feasible?

It does, but make sure you do a file based backup in case there is any issues during the cloning / partitioning operations.