Materials and procedures for painting acrylic (Plexiglass) sheet
As long as the underlying panel will not flex, yes, you can use normal acrylic paints, but a primer is required, and the recommended method is to fine sand the plexiglass to a slight roughness, then cover with primer.

Acrylic polymer varnish is ideally suited to varnishing over acrylic paint, and I'm pretty certain you can use other varnishes.