You'll know that your tank is done cycling when the water parameters stop changing. As for changing the water, I would do a 25% water change from the beginning, every week.
Hehe, yeah, the LFS love to sell you chemicals for your tank. Most freshwater fish are pretty tolerant of a range of pH. Unless you're getting some fancy, sensitive fish (which obviously you aren't cuz that's $), I choose to leave my pH at whatever it is coming out of the tap. Unless it's 9.0 or something you shouldn't have a problem!
You are right about how to add water to the tank. Just add a bit of conditioner to water that's within 1-2 degrees of the tank's water and put it on in. (I know, it's too easy, isn't it?)
Could I ask what fish you decided to go with? The live bearers are always cheap and fun, I love my guppies. I'm sure anyone on this forum who keeps guppies in your area would be happy to give you some for free. My darn ones just won't stop breeding! (solution to this problem: only keep one gender)