SEO work for our online Microsoft Excel Educational Courses

Hi there, We are within the educational sector offering Microsoft Excel training and courses. It is free to join and take the courses, however eventually there are also paid options for those who want to learn additional stuff. Our potential market includes students, professionals - who need to brush up on their skills and others. I would like to know the best way to go about it; maybe mainly target the UK first of all, obviously most people have to use Excel spreadsheets at some point. Would it be possible to get say 10,000 - 100,000+ users joining up and using the course materials for free within the first year for example? Is it possible to give a figure on the number of people who would join up for free within the first 12 months, quite a high number I would have thought? As mentioned there is also a paid option which takes the form of an intermediate course, what percentage of people who are on the free basic course could join up on to the intermediate course? Any feedback and how you could potentially help would be useful and the results that could be achieved... Many Thanks, Harris..