Limit client to order Service based on Configurable option

[supoort tech]

Hello ,

I need help to limit client to order same service for same value of configurable option that i have added.

Lest says i have trial service on which client need to add some username, i want to limit client that for same username order more than one trial.
Also i need to make those fields i add required.

I need at least some direction from where to start implementing this option.

Kind Regards,