Ok hold on a second...
Is this game really PS4 - PC cross-play?
No fucks given about Controller vs M/KB?
Game supports m/kb natively on PS4, so no.
Controller players have significant aim assist so I actually think they are at an advantage if I'm honest. Particularly given mouse users have no way of adjusting sensitivity except through any direct DPI settings their mouse has.
Can't get KB/M to work with PS4 at all.
You need to have a controller on at the same time, you can then switch between the two seamlessly. Remember to adjust the time until your controller turns off setting in the systems settings (Settings > Power Saving Settings > Set Time Until Controllers Turn Off) so it doesn't accidentally turn off mid way through a round.
Note, you can't adjust any mouse sensitivity in game so it doesn't feel quite right at the moment. You also won't have a cursor in menus for some reason (assume a bug). This has so far stopped me remapping any keys (not sure if you even can) as it's a pain in the arse trying to guess where you are pointing and the key mapping screen is just a long list.
No. It's cross-save but not cross-play.
I hope this changes in the future. I'm currently playing PS4 but am moving to PC soon and also have buddies on XB1 so cross-play and cross-save would be ideal for me.