Do I need a Multisite? [closed]

If your client asks for multi-sites, there is no alternate option for it then.

But according to the need, sometimes creating separate pages for clients like website.com/client1/, website.com/client2/ etc. and masking/redirecting client1.website.com, client.website.com to these (respectively) may work as well.

This will lessen the trouble of handling multiple sites.