mate! i was in ur position exactly wen i started as in tht i wanted 2go 2 drama sch and i only wanted to do 3 cos thy were the only subjects i was intrested in, but i took english lang as well just to do 4. but i hated it and dropped it after about 3 wks. you can do the same, no trouble.
as for your job, thts a lot of hrs! 16hrs a wk? i'd say ud be able to do work and as work but you wont have much free time. but if thats wht you want, go for it.
anyways, take 4, give it a go, see what happens, you might perfer all the as levels to ur job!