How can I CREATE characters that are radically 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 piece 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 (or attempt to) your question. Whether you actively 
choose to write characters (& I think we're referring to main 
characters here) whose emotional 'toolbox' or psychological makeup is 
radically different than yours is really immaterial. You may write incredibly intense but self- contained characters that really 
challenge actors to dig deep to express ALL 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 the character you 
want to create.... and 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 characters' emotions need to come from 
a REAL place inside of you that allows you to project all of the 
nuances of that person. 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 and the STORY 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 luck with your screenplay . I’d love to read your work at Wordsmythe.ca