The first thing I would look at for an oily slick, when faced with a new fish keeper, is the fish food itself. Many, perhaps all, new fish keepers overfeed their fish. The oils in the fish food that is not eaten can easily form a surface film of oils on the water. Please take this as an observation and not a criticism, Helen. It takes time and experience to start to correctly judge how much to feed your fish.
I am sure your new acquaintance at a LFS is sincere enough, but nothing short of a filter clone will really shorten a cycle these days. At one time, truly effective bacteria starters were sold as Bactinettes in the UK and as Nitrospira in the US. I know for a fact that Nitrospira is no longer available in the US and have not seen any UK members talking about bactinettes for a long time now. My guess is that both were products of the same manufacturer and were both discontinued because they required continuous refrigeration from manufacture to final use to be effective.
Have you tried looking through the filter media donors that are listed on this forum? The most certain way of getting a proper start for your filter is to get some mature media from an existing filter. I am sure that most of us who are willing to donate media really care about helping new fish keepers get off to a good start and would not hesitate to help anyone who asks. It does require that the new fish keeper ask someone nearby though.