i am a bit lazy to take pictures myself now but here is one from the web
The white spots on the gill cover and the pectorial fin are the breeding stars (breeding tubercles)
The eggs are sticky and will adhere to plants, decoration and gravel. The female will release eggs preferably close to plants (moss works great).
Just remove the plants/ decoration and move them to another tank.
Use water from your main tank and a heater to maintain a temp around 22C. After this use fresh, conditioned water (at the same temp) for water changes. Also make sure that the water level in the egg-tank is not too deep.
Ideally you should setup a small sponge filter to provide some sort of filtration. You can very easily build one very cheap (search for DIY sponge filter on google) and power it with an air pump. You can adjust the flow with an air valve, so that fry are not getting sucked into the sponge.
Alternatively you can do frequent water changes until the fry get larger. At some point you will require some sort of filtration however.
The eggs will hatch within 1-2 days, after which they will still remain at the bottom if the tank, feeding off their yolk sack (~1 day). During this time, remove any eggs with fungus attached to them. These are unfertilized eggs. After day 2-3, the fry should be fed 2-3 times per day.
As about the size, it can vary. Just take a look for breeding stars, which should be an indication that the fish has reached sexual maturity.
Also know that fancy goldfish typically reach their full size at about 1-2 years old, after which they might continue to grow slowly.