Yep, that’s about all you need to second.
sling: 120 or 240 are fine. 120 can be less faff at times but I use 240 as they give more flexibility.
Belay plate to belay your leader and abseil back off if needed. Prusik is not essential but I personally don’t ab without one unless I have to.
You shouldn’t need any more than one small extra screw gate and an HMS to belay unless you are leading or multipitching (it’s only used for clipping you to an anchor)