multi users to certain amount then stop?

Hi. I’m using wp 1.5 on my main site https://www.jakiblue.net, and want to set up another blog on a subdomain. I want this to be multi users – it’s a review site where certain staff can log in and post their own reviews. Now, I know in the ‘options’ panel in admin i can check ‘anyone can register’ (meaning they can then post after i set their user level?) , but once I have a certain amount of ppl register, say 6, do I then go back and UNCHECK ‘anyone can register’ so no more can register? And the ppl who did origianlly register can still continue posting? Is that correct?