You also want a SPDT NO contactor and a swith to operate to be able to shut off main power to the panel (or go with a P-J e-stop, but I prefer the former). Add another set to be able to turn your element off without relying on the SSR not to leak or fail on.
You want some type of GFCI, either an inline cord, spa panel, or breaker.
You may want an alarm buzzer triggered by the PID, and perhaps some type of switch to disable it.
If you are going to add a timer, you may want another switch to disable the alarm buzzer.
That about covers it, but when you have the entire list of components post it for a final review and comment.