Do CoA's show up on your ERB and if so how many are allowed?

Yes, no limit..

Yes they will show up in awards and decorations on your ERB they will be at the bottom of the list. You can potentially earn unlimited certificates of achievement, however only four certificates of achievement are able to be used for points for promotion. Get with your units S1 to turn a copy in for your record of it wasn't already added.

You're limited to 4 COAs for points. They're worth 5 each. See your S1 to get them added.

If I am correct only battalion level and higher COAs count four points though

Sorry I wasn't clear. I was responding to the promotion point piece of the question because I assumed your motivation for putting it on your ERB was to get the associated points. I'm not sure if I would want to overload my ERB with COAs beyond the max that can be used for points though. It doesn't show what they're for so all you would see would be "COA" listed over and over. Just my opinion.

Must be entered by S1.

COAs do you show up on your ERB and also your PPW (DA 3355). You can have as many as you have earned on your ERB and PPW, however, only four of them will count toward your promotion to SGT.

Yes, they do show up. Take your COA to S1 and have them add it to your ERB. You can add as many as you have, but only 4 will be counted toward promotion to SGT.

Make sure they are certificate of achievements not appreciation. Achievements are worth the points

Just make sure they get put in. Otherwise they are like awards with no orders with a copy put in (they don't/won't be counted). I have severals CoA's and medals that were/are like that. Since I had more than enough to max out fairly quick in, I never bothered to fight for them to get official entered in my records.