>>Yes. It's safer to do it in SSMS (specifically I do it visually in a database diagram because it is really easy). You can generate a script once SSMS has done it for future reference.
>
>In Table Design mode you can generate a script w/o applying updates to a table, if necessary.

Yes.

Usually, when I'm ready to create a constraint, I'm ready to apply it. The visual designer just saves me a little effort by allowing me to create a constraint by dragging between fields on tables (still have to confirm/set specifics in the wizard).