
Step one: Determine your reasons for writing. First and foremost, your motivations will help shape what sort of character is a "good fit" for your environment. In the case of writing fiction (that is, stand-alone stuff not meant to integrate with the community at large) there are a lot of plot hooks and designs that flow a lot better: A novella or episodic glimpse at the Warrior of Light works best when it isn't butting up against the entire rest of the RP world, and while any concept can feasibly work with a cool enough group, it can be lonely or isolating to be writing a character that you find amazing while other folks might not be so hot on them.
If you're just trying to write, then yes, go hog wild and do whatever you prefer writing about. If you're wanting to crash into other people with RP and tell stories, it is really important to remember that RP is a cooperative, give-and-take experience. What one writer likes to see might not always mesh with what's best for a community storyline, or sometimes concepts that are relatively abstract ("My hero is the crown prince of another world, and he's cursed to change between the races every moon, and also he commands a giant mecha fueled by the power of friendship. Also he can talk to cats and dogs.") don't allow a lot of breathing room for those you're working alongside.
Sometimes what's best for fiction is not what's best for roleplay, and that's okay.
As for backstory? I've never found it terribly important. I prefer to work backwards from the concept and rationalize accordingly. Pick what tropes and personality traits you want to write, and then determine how they got attached to the character. Canny mage-type? Maybe he was dedicated to reading all he could on the subject as a child. Simple enough rationale that provides more bearing in the world: Reading and literacy aren't particularly common in the smallfolk of Eorzea. He would have been educated and better off than most. That implies wealth and stability of sometime, if he wasn't needing to work to help maintain house and hearth. It's also not a pliable career compared to trade or farming, further emphasizing a more privileged upbringing. It also might reflect on some token hereditary traits of his parents/caregivers also being capable as magic-users.
So we've taken three words (canny mage-type) and then spun off a tiny seed of background, with more room to work from. Maybe his mother was a powerful Hearer but refused to cooperate with Gridania and fled. Maybe his father practiced Black Magic and wants to cement his legacy by having a more powerful child. Maybe his folks promised to cultivate his aetheric nature in a pact with a demon to sacrifice later in exchange for boons.
I could keep rambling but this is already tl;dr enough. Sorry.
If you're just trying to write, then yes, go hog wild and do whatever you prefer writing about. If you're wanting to crash into other people with RP and tell stories, it is really important to remember that RP is a cooperative, give-and-take experience. What one writer likes to see might not always mesh with what's best for a community storyline, or sometimes concepts that are relatively abstract ("My hero is the crown prince of another world, and he's cursed to change between the races every moon, and also he commands a giant mecha fueled by the power of friendship. Also he can talk to cats and dogs.") don't allow a lot of breathing room for those you're working alongside.
Sometimes what's best for fiction is not what's best for roleplay, and that's okay.
As for backstory? I've never found it terribly important. I prefer to work backwards from the concept and rationalize accordingly. Pick what tropes and personality traits you want to write, and then determine how they got attached to the character. Canny mage-type? Maybe he was dedicated to reading all he could on the subject as a child. Simple enough rationale that provides more bearing in the world: Reading and literacy aren't particularly common in the smallfolk of Eorzea. He would have been educated and better off than most. That implies wealth and stability of sometime, if he wasn't needing to work to help maintain house and hearth. It's also not a pliable career compared to trade or farming, further emphasizing a more privileged upbringing. It also might reflect on some token hereditary traits of his parents/caregivers also being capable as magic-users.
So we've taken three words (canny mage-type) and then spun off a tiny seed of background, with more room to work from. Maybe his mother was a powerful Hearer but refused to cooperate with Gridania and fled. Maybe his father practiced Black Magic and wants to cement his legacy by having a more powerful child. Maybe his folks promised to cultivate his aetheric nature in a pact with a demon to sacrifice later in exchange for boons.
I could keep rambling but this is already tl;dr enough. Sorry.