WPMS import User question

Importing users by script shouldn’t be a problem if you are able to do some custom coding to make it work. It also depends on what format the users are in and if there is enough information to create a valid WP user. Unless their password is plain text or a MD5 hash, you’ll need to decide on how to manage new passwords.

Are you creating one subdomain site for 5000 users or 5000 subdomain sites, one for each user? I don’t think there’s a problem either way. If 5000 sites, you’ll need some scheme for naming all the site subdomains so there’s no duplicates. If the answer is several dozen sites with several dozen users each, there would need to be data for who belongs to which site.