Frequently new users will have statements in their posts like "I'm new here", "Rookie DM here", "This might be a stupid question", etc. Like this question. Is it ok to edit out these statements? I'm worried that it may come off as rude to users that are unfamiliar with SE.
Don't remove important context
Whether someone is, by own admission, a new player or gm is important context for a question. Specifically, it helps answerers frame their advice to the kind of querent that is asking. Don't make edits which removes, hides, or obscures this context.
To identify things which are better of removed, try if it retracts from the question. There's no hard line or test to see if something retracts, so it'll be down to a case by case judgement. Stating that you are new to the site specifically is virtually never needed as this is already handled by the new contributor frame around the user mark (which stays for a week following your first post). One of the big things we are editing/polishing posts for are future readers, and you being a new poster here isn't relevant to them.
Using your case as a case study:
The "I'm a very new DM" statement at the start is useful. It should stay.
The rest of that disclaimer isn't necessary, so could be pruned. However, it flows from the way the querent has decided to state they are a new DM and, as it is a seperate paragraph (and italicised), it is easily skippable. Thus it doesn't really noticeably retract from the question and there's no pressing need to remove it.
Having thanks at the end is also something we generally prefer not having as it distracts from the actual question, but as there's only two words at the end dedicated to it, it isn't enough to warrant an edit just for that. There wouldn't be anything wrong with removing it if you were already making edits to the question (and it doesn't break the flow of the text).