I am planning to do one as well but instead of bike seat, I am going to try car seat! Imagine the center portion with carving.......... still dreaming
As for the dye, I am thinking of a coat of shellec to seal the dye in the leather and then a coat of clear acrylic over the top. Is that how it is done? This is if the seat is going to be black.
At the moment, it's a grey seat so I probably have to airbrush grey acrylic to match the colour.
singteck