Have a read of all of these as it will get you started along the way, although it will involve a lot of coding along the way.
https://www.wix.com/corvid/example/Multistage-Form
https://www.wix.com/corvid/example/Custom-Validations
https://support.wix.com/en/article/about-triggered-emails
https://support.wix.com/en/article/creating-a-triggered-email
https://support.wix.com/en/article/about-wix-automations
https://support.wix.com/en/article/adding-variables-with-wix-automations
https://www.wix.com/corvid/reference/wix-crm.html#createContact
https://www.wix.com/corvid/reference/wix-users.html#register
https://www.wix.com/corvid/reference/wix-users.html#login
https://support.wix.com/en/article/corvid-tutorial-creating-a-custom-registration-form-with-code
https://support.wix.com/en/article/corvid-tutorial-building-your-own-members-area
Wix Code API:
https://www.wix.com/corvid/reference/