Aways begin with the lighter colors and after that the darker. I would have started with all the red and after that the black. But yeah interesting model. I would remove all the traces of the molding and glue up the cracks. Where did you get this? Would love to paint one as well
A little tip with painting, thin your paints a bit in a pallet. This ensures they go further and prevents brush stroke lines when the paint is dry. For acrylic paints, you can just thin with water but for oil paints, you will need a specialised paint thinner. Each paint thins differently and starts at different viscosity but you should aim for the paint to smoothly apply off the brush but not flow, generally around 25-35% thinner works well. I would also recommend spraying the model with primer paint and adding around 2 layers of regular paint. The train looks good though and fun, however, I would have spent the time cleaning up the model a bit with a file and modelling clay just for a better finish.
