Please note handles must include the "dot" part. For many people this will be something like "myhandle.bsky.social" at the moment, but accounts with custom domains will have something like "myhandle.mydomain.com".
Bluesky handles only consist of lowercase letters, numbers, hyphens (-), and dots (.).
There are no official numerical user ID's on bluesky. Everyone has a unique, persistent Decentralized Identifier (DID) that usually looks something like "did:plc:ewvi7nxzyoun6zhxrhs64oiz". Checking for new DID's on the various PDS servers of the platform is done continuously, and once they are found, they are assigned a numerical ID. There is no guarantee that this always works well, so please regard these twexID's as best efforts to give you a sense of how many accounts were registered on Bluesky.