The issue was raised elsewhere about whether commercial plugin developers would still support their products if they log into your site and find you are using CP.
It’s obviously too late for existing plugins that you are using, but for future purchases I think it would be a wise move to contact the developers before buying, tell them you are considering using their plugin and ask if they will support it being used on CP. You could also explain about the similarity between CPv1 and WP4.9.
This will have two advantages:
It will cover your back in case you need any help down the track
It will show the developers there is interest in Classicpress