Do you need a stop bath for b/w film development?

Short answer - no.

Well then, why do stop baths even exist you might wonder. Well, it's like this - when you pour out the developer you don't get every drop of it out. When you pour water in, it's just diluting the stuff that was in. Even if you're fast, this might take 15-20 seconds. If your development time in total is just a couple of minutes, then this will have a huge impact on your results. In those cases you do need a stop bath, to kill the development process instantly.

So long answer, yeah, it's good to use it if your development time is <5min. I have never used such a short time.

When it comes to paper, it's more about prolonging the life of the fixer and not bringing in any active developer into that tray.. so why not, stop baths are cheap.