I had a captain suggest to upgrade WB FO first.

If you love it, stay.
But if you hate it, or just can't get used to the sleep schedules or whatever ... you have an option to break seat-lock and come back to the NB side of the house with an upgrade to NB CA.

Side benefit. Done in this order, one is far less likely to come down with a case of the 'what ifs?'