If I have myname.com, Can i setup on subdomain: subdomain.myname.com ?

Instead of setup for clients, can we just give a special link URL (with our own domain name), where the clients can register on their own, then the clients do the WhatsApp setup on their own?

Can the clients also create the landing page on their own?

Can the clients have their own portal, to manage the leads on their own, and manage/analyze the data on their own?

Thanks.