Yes, use microballons and silca. Microballons by themselves won't act as a thickner and it'll run on vertical surfaces. Also, I used a cabinet scraper, available from woodworker stores, between coats to remove the high points. Whether you use a scaper or sand, do it as soon as the epoxy has set up - not tacky, and sandable (doesn't form gummy clumps on sandpaper). If you wait too long, especially with silac in your epoxy, it will take more effort to sand it smooth.
One last note, you need to finish with a coat of epoxy without microballons to proper seal the finish.