Hi, I'll try to answer your questions:
Would you advise a small business owner to have their product certified after the 93/42 ewg? - if you want to sell a medical device in Europe today, it must be CE Marked according to 93/42/EC today. Going forward, the MD Regulation will take over.
Is ISO 13485 mandatory or not? - No it is not mandatory, however you must have a quality system. The extent of the Quality System depends on the product, its classification and the chosen conformity route.
Is it even possible to do it without much prior knowledge? - Unfortunately, it will be difficult without prior knowledge, either within your company or by using a consultant.
Chris