Hi dear Wintek! Planet Hanyu has organised before virtual Pooh rains, however in the traditional way after Yuzu skated in competitions. The first time was here:
and the last time this one:
So maybe you could use the existing hashtag because having his name in it, gives the hashtag more visibility (you could also just add his name to the hashtag you have created!).
The other hashtag regularly used is #LoveYuzuruFromAllOverTheWorld but you should have max. 3 hashtags in your tweet, so you have to pick up carefully which ones you will use.
Also, if you are encouraging people to share their favorite Pooh fanart as an option, please add that it should be properly credited...people sometimes tend to forget it and just use the image.
Regarding the date you want to do it, is there any particular reason for it? Because another possibility would be to use it the day the assignments are out and thus truly welcome Yuzu into the new skating season.
You have mentioned this: ‘Bombard’ social media with alternative content to counteract negative messages and fake news circulating around." The Pooh rain has always been a special tradition to show Yuzu our love just after he skated. I think it's a nice idea to "welcome him in the new season" by doing it one time but it's not suitable to use it to "bury" content or fake news circulating in the internet just any other day. Yuzu has said he loves to see the Pooh rain, so I think we should keep it just in its "pure original" form (to say it somehow!) for the times he just finished skating his programs, preserving and protecting it the way it's close to his heart. Maybe you meant it just as the first test and it's not your intention to use the Pooh rain hashtag every time, if so, please just disregard what I wrote before.
One last small detail, I think it should be "Fly Yuzu! We ..." and not "Fly Yuzu! we..."
I hope you don't mind in a wrong way my suggestions. I truly think it's a lovely idea.