That's a good idea: split into both September
and October.
The slides that I have presented in the past mostly cover what you mention below, but:
a) they definitely need to be updated for 2022 (e.g., have to wait for 2022 Hacktoberfest logos and whatnot to become available)
b) they could be expanded for some of the things you talk about below
That being said, over the past few years, the people who have attended this Hacktoberfest talk about been 100% Git newbies. I tried to keep the presentation to be the basics -- I stayed away from merge conflicts, cherry picking, ... etc. There were typically enough questions and whatnot over what I presented to fill 1+ hour.
So far, I have copied my slides from last year and put big yellow boxes on the pages that need updating for this year. Do you want to collaborate on this year's slides? I'll share the Google Slides link with you.