I own Hitman 1 on disc and played it on my PS4. My girlfriend bought Hitman 2 digitally and I played it on her PS4 with my PSN account. I will be buying Hitman 3 on disc. Even with all that detail I'm not sure if I can unlock the previous game content in 3 without paying for it again
A little frustrating that the install will be so big because those previous 2 games are included but I can understand why they've done it. It will be annoying though to have content I own taking up space on my hard drive but being inaccessible!
I won't carry over progression though. I didn't with Hitman 2 and I think it was better for it - starting with a limited loadout and unlocking stuff as I went rather than immediately having things like an unbreakable lockpick or electronic hackers.