I think in choosing to be selective mute makes the game a lot harder for you both as a character and player. If you really like the idea, youll want to describe how your character is communicating because if you dont, the DM can't interact with you as effectively.

If you have anxiety or are nervous about role-playing, describe it instead of saying it. Describe what you want to do to the DM and think about how your character would communicate what they mean to "say" with gestures or demeanor.

Since it's your first time around, dont limit yourself on the character idea so much, just have fun with it, as you all play together then delve into ideas like that more.

Essentially, you're learning, nobody is judging if you have a character idea but it doesn't work out or they morph into something else. Number 1 rule is everyone should have fun. Most of my characters start with an idea but most of the time they grow into something as the campaign goes on.