Do you really think there will be a big rush on Lemmy's servers on July 1st? In my opinion most people that wanted to switch to Lemmy/boycott Reddit already did so. The rest will just use the official app or the browser website.
Thankfully, I don't think Lemmy needs millions of active users to be good. Even currently there's more than enough content for me and I still expect it to grow
I think there won't be an immediate rush, but I do think there will be a sporadic sine wave of people checking out the place.
Funny enough the best thing people can do is hold off posting memes and then doing it on the 1st of July for maximum engagement.