Welcome to R2R! As @bnord said. A skimmer is optional, especially in a smallish tank. Use the money you would have spent there to get some good test kits for your water parameters. You don't need to be fancy but pick a good brand. Salifert is probably the best for price to performance in general but there are lots of good kits. For cycling the tank you will need a refractometer or hydrometer (to measure the water's salinity), an Ammonia test kit, a Nitrite test kit and a Nitrate test kit. You will not use the Ammonia or Nitrite test kits often once your tank is mature but the Nitrate test kit is one of the fundamental tests that are run often so pick a good test kit. There will be more kits needed but those will get you through start up. Also don't use tap water for your tank. Either buy/make RODI or buy distilled water. You will need this water to replace water that evaporates and to make your saltwater unless you buy the saltwater pre-made. Good luck and have fun. Above all else be patient and take your time.
