I agree, you'll be fine. I'm in a similar position, having just completed my GTP in music, whilst at the same time teaching Performing Arts, English and Dance. I'm doing similar this year, just with no English, but more Drama. You won't have to write SOW for the other subjects I assume, and most good HoD's tell you roughly how you should be navigating yourself through the SOW's anyway, so that's your weekly planning done. It sounds like a lot to cope with, but you'll be fine. Keep in touch and shout if you need anything, I've made it through and am relishing the thought of getting stuck into my NQT.