I forgot my iPhone passcode. After restored it, all data will be deleted?

Without a backup, no the data is gone.

Anything sync'd to iCloud or other providers' clouds like Contacts, emails, calendars, reminders, maybe Photos if you had iCloud Photos turned on, will return when you set it up with those accounts.

No, your phone data is already scrambled, it's gone.

Yes.

You will hopefully have iCloud Backup turned on?