You don't want any sudden changes in surface height as these will cause bridging and bubbles. Remove hi spots and if there are any spots too low to get rid of by removing material, you can fill them. You don't need super-smooth, but you want the surface even.

Don't be sloppy with the epoxy because sloppiness usually means more resin than you really need to get the job done and that translates into excess weight. Being neat pays off in saved weight.