Yes you want to bring your ammonia back up to 4ppm so that your nitrosomonas (bacteria that feed on ammonia and produce nitrite) don't starve out. So you want to keep adding ammonia to keep it at about 2 to 4ppm to feed those bacteria while you grow the second bacterial colony (Nitrobacter the ones that convert nitrite to nitrate).
Have in mind that very high nitrites and/or nitrates can stall your cycle (the ates less so than the ites) and by that I mean nitrites not much higher that 10ppm and nitrates below the max reading on the liquid test kit (160ppm I think it is)
You have the high nitrates but since your nitrites are pretty low (and the bacteria are less sensitive to nitrates) I wouldn't do a PWC yet, wait until your nitrites hit like 4ppm then do the PWC and then most likely you wont need to do a PWC until the large one once your tank is ready for fish. Also when you the the PWC simply take out and replace water, no vacuuming substrate or cleaning the glass on the inside or anything like that.
Best of luck =)
