Good evening Rachel and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
I would love to help you with these questions.
Is it possible to remove certain fields from the Community Event Submission page?
Yes, absolutely. CSS is a great way to achieve that.
As an alternative, you can simply create a template customization and remove the undesired fields.
You might want to read our Themer’s guide to get a sense of how that works.
Your second rule is a bit too generic. I would recommend using #event_tribe_organizer and #event_tribe_venue instead.
That being said, keep in mind that the organizer field is actually a required field by default for Community Events. But you can tweak that by reading what is here: https://theeventscalendar.com/knowledgebase/required-fields-for-events-submission-form/
Also, is there a good way to add notes or welcome text to the top of this submission page? Thanks!
Yes absolutely. To achieve that you simply need to do a customization using our Themer’s guide (referenced above).
Let me know if that helps.
Have a great day!
Geoff B.