Can you transfer and use mods from a PC / laptop to the PS4 with a USB stick?
No, you can't.
Not possible. It is discussed whether it will still be introduced for games like Sims 4, but very unlikely.
If you have a DEBUG PS4 with Linux program, yes.
No, that is not possible unless you have a jailbroken Ps4
Yes it is, but it is very complicated.
Do you know a Youtube viedeo?
Unfortunately not.