1 I don’t know how much for this is possible or meaningful given that Sync is end to end encrypted and we are talking of files that ultimately are on your hard-drive. It’s something to think about. Feel free to open a new feature request about this specific point.
2 There is a plan for Sharing with with Sync https://forum.obsidian.md/t/vault-sync-sharing/16085 and There is a FR for Self hosted Sync https://forum.obsidian.md/t/self-hosted-sync-server/20975
3 & 4 .There is an official documentation and plenty of youtube tutorial and courses.
5 Yes, there is publish for that and there is also a FR for private site generator https://forum.obsidian.md/t/enterprisey-private-publishing/9340