ODOO v16. 

I'm building a FORM on my website for volunteers to sign up for an event. 

I need them to be able to choose an available SHIFT. Once a set number of people have signed up for a particular SHIFT , I need that SHIFT selection item to no longer be available for future people signing up. 

Don't care if it's a radio button or checkbox or drop down.... 

Don't care if it's creating a TASK in a project or CRM opportunity, just need to able to set a quantity limit of available SHIFTS. 

Ideally want to be left with a exportable excel/csv file of the volunteers who signed up as well, so leaning towards TASK or CRM destination. 

Any wild ideas?