What are the consequences of having a work and personal iPhone with the same Apple ID? I'm considering having both a work and personal iPhone.

The phone numbers will be different, but I'd like to use the same Apple ID for convenience.

But I'm concerned about possible cross-pollination. Presumably text messages will be separate, but things like apps and photographs will be the shared. Perhaps iMessage texts too?
You can use the same Apple ID and as you wrote, apps, music, books and so on are shared between devices.

Regarding Photos, you can turn on/off syncronization (Settings -> [your name] -> iCloud -> Photos, then turn on/off iCloud Photo Sharing)

Regarding iMessage you can turn on and/or off this feature from your phone (Settings -> Messages)