In my case, I did stage 1 on the 1st of August, stage 2 on the 5th of September and then waited until the 28th of October to have stage 3 in Belfast (I could have done it earlier down in Fareham/Swanwick but I was working abroad the other dates that suited me). As far as I know, the January course is full so they are talking about starting in college in April or July.
Regarding visits, I went to a couple of aerodromes, one NATS (Aldergrove) and one non-NATS (Belfast). I also went to have a look at the Scottish and Oceanic ACCs, which I found very interesting, especially comparing them to what I had seen at the aerodromes.
Hope this helps.