My melody and harmony is playing piano sounds.. since both are same instrument, is it a good idea to compose them in same clip??
You can, there is a lot of music which has this. Pro musicians do this all the time to intergrate melodic ideas within their harmonies. but ideally if unless you are already pro a at composition, we encourage you to stick to different tracks, as suggested in the course get comfortable building out an arrangement. Then later will naturally begin to stray away from this format, to make it your own!