Berlin filtration method requires a skimmer, strong flow, strong light, live rock and a sump or filter for mechanical filtration (only mechanical and chemical). Many people take this a step further and have algae in the sump for nutrient export.
As you don't have a sump you should use the filter but rinse or replace the media often in pure RO or tap water to kill off any nitrosomas. If the filter matures in a standard way it will start to starve the live rock which could result in a reduction of its effectiveness and an increase in nitrates.
Quality live rock deals with waste, ammonia, nitrite and nitrate from a series of organisms that inhabit it from small crustacean down to anaerobic bacteria. The strong light encourages photosynthesis which is important to some of the live rock inhabitants and aids in the process. The skimmer removes organic proteins before they break down into ammonia, with the berlin method it's essential you don't skimp on the skimmer. The sump allows surface skimming to remove the oil film as well as mechanical and chemical filtration, a place to hide equipment and keep macro algae. It also acts to keep the display tanks water level constant. A filter will only do part of this but it can work. I'd keep it as somewhere to run rowaphos and/or carbon when the need arises.
Coral sand can be rinsed in RO water, not tap.
The guy in the shop... 1/ get zero TDS RO, fill tank 50-75%, run for 24 hours to ensure that equipment works and tank doesn't leak. 2/ drain tank again and add egg-crate and coral sand, refill tank - if the RO is still zero TDS it can be re-used. 3/ Add measured quantity of salt to bring to correct salinity slowly. Ensure it all disolves and use a refractometer to check. Leave another 48 hours minimum and recheck salinity, ammonia, nitrite, nitrate, kh, po4, mg, Ca 4/ Assuming all is working and everything is within NSW ranges go and buy the live rock. Transport it wet (wrapped in plastic is good enough for short journeys. Get it to the tank as soon as possible and arrange carefully. You can use acrylic pegs, milliput or cable ties to get it pinned in place. 5/ Top up the water with salt water mixed from zero TDS RO and your choice of salt. Premix the water for several hours with an airstone. 6/ Monitor the test results daily at first and then twice weekly or weekly as things settle down. Do a water changes often to keep ammonia and nitrate low during this time as this will preserve the life in the rocks. Once ammonia is staying low add a little (tiny amount) fish food daily to keep things alive and continue to monitor.