Is "this 'Joshua' character" a crude way of talking about someone?
Solution 1:
"This xxx character" can be a little derogatory, depending on the context.
For example, "My son has started hanging around with this Joshua character and ever since his school marks have suffered".
However, if you know Joshua and you are obviously friends, then I think it is fine to say: "Since I got to know Aditya, I had been hearing about this 'Joshua' character, who ..".
As a native speaker, I wouldn't read this and think that Joshua was in any way shady, nor, if I were Joshua, would I be offended.
If you are looking for an alternative, you could say "someone named Joshua" which is more neutral. But as mentioned, I don't think this is necessary.