Can we add a new Cassandra 3.11 DC, upgrade it to 4.0, then eventually get rid of the old DC?

Question

We want to upgrade from cassandra 3.11.12 to cassandra 4.0.2 using multi DC replication. We want to do that for easy and quick rollback (avoid a situation of backup\snap and restore).

Steps we think to do:
1. lock app to use (read & writes) only with old\current dc (using driver options).
3. create new dc with same version (3.11.12) - new dc will created with 16 num_tokens (today we are with 3.11 default 256 and want to move to 16).
3. sync all data\keyspaces to new dc - and keep the sync active to the 2 DC's.
4. upgrade the new dc from 3.11.12 to 4.0.2
5. after step 4 done, move app to use only new DC (version 4 after upgrade)
6. wait few days to see all going well
7. stop replication to old dc
8. remove old dc nodes until and stay only with the new DC (cassandra 4.0.2)

A. The main question is this process should work?
B. Is there a problem with move to 16 num_tokens this way?
C. Is it ok to keep sync the data\keyspaces between the 2 DCs for a few days while they are in different versions of Cassandra (dc1 in 3.11.12 , dc2 in 4.0.2)?

Note that I have seen that it is not recommended to have a cluster with a mix of cassandra versions but this is only for an upgrade process with a quick and simple rollback. The old DC with the old cassandra version will be removed after a few days when everything seems to work properly with the new version.