Is a skype number required?

who is proposing to charge you for the skype # ?

Yes you can do a video call for free on Skype without a skype number. I have done that quite often.

When you get a free account on skype, you sign up with a skype name (your logon). Then the other party can search for your name, connect with their own skype and video chat, all for free.

It costs money to call a regular phone with your skype. But using skype to talk to another skype user is free.

Is there a chance that this prospective employer is scamming you? I don't know the details, but something about this makes me a little suspicious.

Every legitimate company I have ever interviewed with pays for all the expense of interviewing. You should never give money to a prospective employer.