I think you have taken up a good initiative. I support this.
There is a repository or I think a nextcloud folder with current Krita assets like logo etc. But we need to have permission from @halla and team to use it. There is a krita instagram handle which I think is not active now.
Youtube is handled by @RamonM as you know.
There is also KDE wide promo team which helps us in spreading the word when there is a release or announcement. I think @Bro666 handles that. so we can may be ask for advice from them.
Krita-artists social media is handled by @sooz
I think it would be great to have a chat with the team on matrix or IRC. That way the co-ordination would be great.
A major complaint on Krita unofficial discord by some people is that we do not make social media posts about upcoming features or any announcement. May be short video or explainer videos or any artist showcasing krita. Of course doing this needs a dedicated marketing manager or a person as devs do not have the bandwidth to make videos and handle the social media thing. @Deevad helps in making what is new video and also makes short videos showcasing the features every now and then.
As you can see everything is volunteer driven and right now is a bit scattered it would be best to tie it all together with the help of people who are already doing things and forming a consistent voice.