Can i use apple watch series 4 without a cellular plan?

Yes you can. It will work just like the Apple Watch GPS versions, or you can just purchase the GPS only version.

Unless you are referring to the ability to activate an Apple Watch with the iPhone. You would need an iPhone that is activated to be able to pair and use.

Not sure exactly what you are referring to, that is why I provided both.

Yep! You don't need to activate any cellular plan and it won't give you any trouble for not adding one.