Just to clarify, your posts don't disappear when you switch servers. They still exist on your old server, and when people click to see who wrote them they will be redirected to your new account profile.
You need to untick all of those boxes if you want to stop all the email notifications? Also you need to press the save changes button at the top right after you've unticked them.
Do you want to schedule your posts on Mastodon? There are many options you can use to do this.
Some third party apps including Tusky and Fedilab have a built-in scheduling option. Fedilab also runs a website at https://plan.fedilab.app which lets you schedule posts.
If you want a professional scheduled post management system, there are third party commercial services such as https://publer.io and https://buffer.com that now include Mastodon compatibility.
As for DMing people, you'll have to message them on other platforms because by definition they won't be on here yet.
You could for example generate an invitation link and post this on your social media elsewhere (Facebook, Twitter etc)? You can generate links that work for multiple people. That way you don't have to send out lots of messages either.
Posting hints and tips about Mastodon and the Fediverse ๐ There are lots of answers to common questions about Mastodon and the Fediverse on my website at https://fedi.tips. If you can't find your answer, @ or DM me and I will try to help! There's no such thing as a silly question!I am a volunteer, you can buy me a coffee at https://ko-fi.com/fedithing or become a patron at https://liberapay.com/FediThingMaintained by @FediThing, banner artwork is by @posiputt