Thanks so much for the replies so far!
Few questions I have -
1 - I'm grasping the concept of fish less cycling now I think. Basically it seems we're trying to kick start the bacteria forming in the filter and in the gravel etc before we actually add the fish - thus giving us a stable environment rather than an up/down one when we first add them? And we're using ammonia to kind of imitate the waste the fishes would usually produce? One thing I don't quite understand yet, is how does just adding ammonia to dechlorinated water start this cycle? And can I have the ornaments / live plants in the tank at the same time?
The ammonia won't harm anything if dosed correctly. So yes you can have plants etc. However, having plants makes it difficult to monitor the progress of the cycle, so they're best left until the tank is cycled. Their needs are also not necessarily complementary to the needs of the bacteria during the cycle, so again, leave them until the cycle is done.
Ammonia is the food of the first type of bacteria we need to cultivate. They eat ammonia so that when we introduce fish they eat the ammonia produced by the fish.
2 - with water changes, I presume it's easy to dechlorinate the water I'm putting into the tank? and once the fish are in - are they ok with the temperature drop that this will surely temporarily cause?
You match the temperature of the new water to the tank water by mixing hot and cold. With experience you'll easily be able to do this by feel within plus or minus 1C.
3 - is the best thing regarding the light on the tank to run it on a timer that, for example, puts it on for 12 hours - then off for 12 - then on etc? I presume the filter and heater are always on?
Filter and heater always on. light on a timer a good idea, but max 8 hours and reduce if excessive algae.
Thanks again!