Writing someone other than yourself.
Do I really have to be able to create characters that are wildly different than me?
Your question strikes at the very heart of the writing experience.... do we only ever write ourselves into our creations or do we consciously choose an alternative route and try to write something other than ourselves and our own experience? Now, many people will argue that no matter how hard you try to write outside yourself.... You are in every single thing that you write. And I sincerely hope so, it is your creative energy that makes a piece or character 'live' and breathe on it's own.
But to answer your question, it doesn’t matter. You actively choose to write characters whose emotional 'toolbox' or psychological makeup is radically different than yours. Or you may write yourself into every screenplay (Think, Woody Allen) You may write incredibly intense, but self-contained characters that really challenge actors to dig deep to express all that these characters are with just a few small gestures - because that's who you are. Or you may study minutely the mannerisms of people you meet that are like who you want to create in fiction. You bring life to a character on the page that mirrors those mannerisms, even though they are not your own.
You don't have to be a wildly emotional person to create that kind of character on the page. But your character’s emotions need to come from a real place inside of you that allows you to project all of the nuances of that feeling. So you make a study of people you meet that are like your character...and build on that - starting first and foremost with actual emotions - love, hate, anger, jealousy. But I want to reiterate - wildly emotional or intensely withheld doesn't matter.... write what suits the character you're creating.
And if you choose to focus on a particular 'type' of character.... and you create a series of films about people who are bright, articulate and very considered with their emotional displays.... actors & audiences will still love them if they are well drawn and bring us stories that illuminate for us something of our own lives.
I hope this helps. And I do wish you good luck with your writing.