Hello !

Thank you very much for all your advices, it's very appreciated !

I'll do exactly as you say

Right now, I'm applying some good sealer I have, with a light sand using 000, and the result is already astonishing ! It brings more contrasts to natural wood, keeping a "root" side, I love it !! I'll glue the neck later.

About the bridge, I'm checking all hardware stores and wood factories around me but these specific inserts aren't easy to find (and I'm bored by online stores for now ). Anyway, I have time before inserting the bridge and electronics.
If I really can't find long inserts, maybe I'll glue the hole and its bottom (with wood glue or ultra glue) : it will hold but then I know it'll be an issue if one day i'd like to replace it (for now I won't). Don't worry I promise to not do this in the first place !!

Thanks again for the answers about the fingerboard and pickups, it's more doable for me now

Just a small question :
I need to connect the ground wire to the bridge (I see the small hole !) : can I just put the wire there with its end nude, and then insert the insert in the hole so they will touch each other ? Or do I need to solder both parts together (but how ??).

See you !
Roger