How to have a smooth migration

Hi,
Its postgres database behind the scenes.

We have a use case in which the customer is planning to migrate data from
an older version (V1) to a newer version (V2). For V2, the tables will be
new, but their structure will be similar to the V1 version with few changes
in relationship might be there. We want to have this migration approach
happen in multiple phases in which each time the delta data from version V1
will be moved to version- V2 and then final cutover will happen to V2 if
all looks good or else rollback to V1. The tables are smaller in size like
max ~100K records in tables.

My question is, is it a good idea to have an approach in which we will have
procedures created to move the delta data in every phase and schedule those
using some tasks for each table. Or any other strategy should we follow?

Also another thing to note , we have used sequences as primary keys in some
tables and they have FK relationships with other tables, so the same
sequence number in version V2 will cause issues/conflict, so how should we
handle this scenario? Should we just create new sequences with higher start
values?

Regards
Veem