I like the crankset.
Glad you didn't repaint the frame.
Why not both brake levers? At a minimum, the available hand positions and grip would be symmetric.
The disc brake is not a good idea. You'll need to replace/buy the front wheel (hub and rotor), the fork (meant for disc loading and mounting), the brake caliper (let's say mechanical caliper), and the brake lever (in all likelihood, but I can't confirm from experience between road levers and mechanical disc levers). For what, exactly?