REGEX / if else/ Email optional? / Legend customization

So I have to design an e-Appointment system for Ministry of Education(Singapore). but the current phase is still in the prototype and bought the Appointment+ recently, testing out on my localHost on my WP. I've fulfill as much requirement as possible but I have a bunch of requirement left, hoping you guys could assist me with this.

1) REGEX for a field in a form; is there anywhere I can edit to implement it on an added fields?

2)Is there a way to dynamically change the form based on the service?

example: if said service is "others" the client needs to fill in additional form to state purpose of visit.

3)Can email be available but not required? is there a way to edit this?

4) CSS/ design question, Legend for calendar ( FREE / BUSY / NOT POSSIBLE) can the word BUSY be edited to something else?

That's about it for now, sorry if its overwhelming or not elaborated enough. Hoping to hear from you soon.

Thank you,
Zamir