I know very little about the Star Wars universe, so take what I have to say however you will. To answer your question in short, yay to heavy mix of both original and canon characters.
That isn't to say I'm absolutely clueless on fanfiction in general. One thing is to consider the time period you're setting your story in. Is it during (forgive me for my lack of knowledge) Darth Vader's reign of terror? Is it during a canon part of the Star Wars Universe? A prequel? A sequel? This is important, as depending on the time period you have more or less freedom on how to write canon characters. For example, if it takes place after the events of canon Star Wars, then you can have characters deviate from their 'canon' archetype. From a minor thing to [blank evil character turned into neutral/good character] to something drastic, like the enslavement of the entire Wookie species to which Chewbacca is now the leader of, this is a way you can breathe new life into canon characters.
If the time period is something specific to the Star Wars universe, then you probably would want to stay to the roots of the character. Unless you're doing an 'alternate universe', but if so, that's your problem you can solve.
You said you aren't thrilled about shoehorning in characters, so your mind is pretty much already made. Writing should be fun, and if you aren't enjoying what you write, it'll reflect in the quality and overall passion you have.
As you're making original characters, just please give proper development. Obviously a character that appears in five pages doesn't need as much as a character that is a foil. What I'm trying to say is that describing the shade of blue skin and illustrious, stunning pink hair that shines brilliantly under the moonlight's bright gleam for a character that'll die in random battle 152 isn't necessary. You know that, just putting it out there.
As a last note, I'd just briefly brush up on round, static, flat, etc character types. Just so you have a basic understanding or review on how characters are classically written.
Good luck on crafting your story.