Here’s a command that shows the number of users and ops on a channel.
(defun erc-cmd-HOWMANY (&rest ignore)
"Display how many users (and ops) the current channel has."
(erc-display-message nil 'notice (current-buffer)
(let ((hash-table (with-current-buffer
(erc-server-buffer)
erc-server-users))
(users 0)
(ops 0))
(maphash (lambda (k v)
(when (member (current-buffer)
(erc-server-user-buffers v))
(incf users))
(when (erc-channel-user-op-p k)
(incf ops)))
hash-table)
(format
"There are %s users (%s ops) on the current channel"
users ops))))