Q: is there a minimum PUM image required to be able to switch to Classic Plus components/pages?
- - Classic plus is a PeopleTools feature, I think since you are already in Image HCM 23 & FIN 24, you can go ahead and upgrade to 8.56.
Q: If we upgrade to PeopleTools 8.56 will we have the ability to invoke/check on classic plus for some components (even if we are not on HCM 9.2.024 or FSCM 9.2.026)
-- you should be able to enable classic plus feature at the component level.
Since, you are already in the PUM: (HCM 9.2.023, FSCM 9.2.024) image you can upgrade the Tools Version to 8.56 be able to switch to the Classic Plus components/pages.