I am a HUGE fan of Ammonia cycling. The best place to find 100% pure ammonia is a pharmacy.
DON'T let fish, shrimp or other organisms rot into the tank to get it cycled. You will most likely introduce harmful bacteria that will make your life later on a lot more difficult.
And note that most people use way to high concentrations of ammonia for the fishless cycle. Most people recommend using 5mg/L for the cycling process. I found that this is way too high. I recommend using between 1-2mg/L for the cycling process.
That also depends on the number of fish you want to keep. For instance if you want to fully load the tank immediately after the cycling process then go for a higher concentration of ammonia. However if you choose to cycle with 5mg/L and then stock with only a fish or too, the huge numbers of bacterial colonies created by the high ammounts of ammonia during cycling will simply not have enough ammonia to feed on after the cycling is over.
So a rule of thumb. More fish --> Higher ammonia cycling

And if you do fishless cycling there is absolutely no need to wait until you introduce your fish. You can fully stock the tank IMMEDIATELY.

Well, yes of course. However, the drop of ammonia/nitrite after a spike, indicates that nitrobacter and nitrosomonas cultures are doing their work. So once their concentrations drop to 0 they will actually stuck to 0. Unless you do something terribly wrong to kill the bacterial colonies (if you wash your biomedia with chlorinated water for instance).

i feel sorry for your fish ... having to swim around in ur piss.... there are products nowadays readily available in pet stores that will start the cycle process... you can pick them up for under 10 $.....