Here is the basic of fishless cycling in a nutshell so to speak.
Dose system to an ammonia level between 1 and 2 ppm
then wait and test till ammonia levels start dropping.
If the ammonia levels drop below 1 ppm and the nitrite level is still below 1 ppm, then dose again.
If ammonia or nitrite levels are still high then wait and keep testing.
Eventually both ammonia and nitrite levels will drop.
Then dose to 1 ppm again and see how long it takes for both ammonia and nitrite levels to reach 0 again.
Once you get to the point where you can dose to 1 ppm and have both ammonia and nitrite drop to 0 within 24 hours, then the system is fishlessly cycled.
If you are going to get fish early, then quit dosing. You don't want to put new fish into a system when the ammonia or nitrite levels are high. Add salt and extra air.
There have been reports that the bacteria that convert ammonia to nitrite establish quickest at a higher ppm than 1 or 2 of ammonia. Like I think I once heard 5 ppm. So perhaps for a first dose, bringing the ammonia up to around 5 ppm might do some good. However, I've never cycled that way and I've also read that high ammonia levels will inhibit the next phase of the nitrogen cycle until the ammonia levels drop, by which time one is likely to have nitrite levels off the chart. I managed to cycle a system fairly quickly during cool weather using the dose up to 1-2 ppm method.
So what ammonia source do you use and how much do you use? Well I can only really comment on what I know personally. I use humonia or Pee if you will. I generally put it in an old water bottle and seal it up for a couple weeks before use. Aging the urine allows the urea content to convert to ammonia. This does two things, 1- it kills off most e. coli that teds to get into urine from our own skin and 2- the already converted ammonia makes dosing easier without the risk of overdosing that is common with fresh pee. People will often pee in a system and then test the next day and see no ammonia and figure more pee was needed and so pee again, and again and again then suddenly the ammonia levels spike and just keep climbing off the charts as more and more of the urea is changing into ammonia. Basically there is a delay with fresh urine.
I found that About one pee worth a day will be more than enough to cycle a system. For my barrel ponics system I usually dosed with about 200 ml of aged urine but I didn't need to dose every day. Let the test kit be your guide. For my big system which had about 600 gallons of fish tank at the time of fishless cycling, I used between 200 and 500 ml per dose and again, I did not dose daily, only as the test kit indicated I should.
If you are going to use a non pee ponic ammonia source. Please make sure you get pure ammonia that has not other additives like fragrance, or soap, or detergent that could have the effect of killing fish/bacteria when they get into the system. I personally don't know of any safe sources of such an ammonia product to recommend.
I have also heard of people using urea fertilizer to dose a system, warning urea is gonna take time to convert to ammonia, it is kinda like using fresh pee. Over dosing is common with urea for cycling. See if you can find someone who has used it to recommend how much should be used. Fish emulsion will also break down into an ammonia source but again, it will take time. I guess anything high in protein that will rot can become an ammonia source but I kinda recommend against putting lots of rotten stuff into an aquaponic system that is new as it is difficult to tell what sort of negative things you might also be introducing, it would be difficult to measure and the smell might be nasty.
Fishless cycling is less stressful than putting new fish into a new system and then having to test and watch and restrain ones self from feeding the hungry beggars. If you miss a day of testing during fishless cycling, no worries, there are no fish in there to be killed. If you overdose, generally the worst that can happen is you need to wait longer or perhaps do a bit of a water change. If algae gets going, no worries there are no fish to suffer from it, just cover the tank. If something goes wrong with the plumbing in a new system while it is fishless cycling, well now you know what needs fixing before you get fish. See, far less stress.