Yes you can be self employed but it's not that simple a four week course will teach you the basics of how to do the job but then you need experience to be able to quote and carry out work.With the downturn of the building industry at the moment there will be hundreds of plasterers chasing the remaining contracts and believe me it is who you know rather than what you know that gets jobs.A 6217 piece of paper might get you a job but it's unlikely to win you many contracts.Walk before you start running .Being a self employed plasterer is a lot different to being the owner of a plastering firm.