Kif or "Kief"..also known as pollen in parts of Europe is just Trichromes knocked off of buds through a screen. Trichromes are essentially just little THC crystals. If you made butter from Kief you would have some very nice quality canna-butter for sure. The finer the screening (less leafy matter) the better quality Kief you end up with.
To make butter from it, I would use a double boiler system of some sort. You can ghetto fab it with a smaller pot floating in a larger pot. Boil the water in the first pot and then add your butter (make sure its REAL butter, not that marg crap, THC binds to fat molecules). After your butter starts to melt add in your kief. Iv'e never done this so I couldn't tell you how much ratio wise here.
DO NOT let the butter burn, stir the butter constantly and do so for about 20 minutes give or take. Since you are using Kief...i would think no straining of any sort is needed. So let it cool in the pot for a while and move it to a safe container. Let it cool to at least room temps before putting a lid on it and then refrigerate.
Well, for your first question...thats going to depend on strain and how well it was grown. Some strains just don't produce as many crystals as others, and when plants are say given warmer night cycle temps than day cycle temps...crystal growth is stunted to all hell. This is also going to depend on what quality of Kief you are going for. The finer the screen, the more material it will take to get the desired end amount. Once again, depends on if you are Keifing all material, buds, leaves etc..or just leaves. Buds will obviously give you more Kief, but then they (buds) wont be as potent either.
Keep in mind you are talking about using Kief. Your material is much more concentrated than what you will see in that post. He is using trim it looks like (mostly leaf). Which is why he is using so much per stick of butter, and letting it simmer for so long (also why I said double boiler). I was thinking that about a gram of Kief or so per stick would be good.
If you properly dry your leaf etc, and keep it away from being exposed to a lot of air ( vacuum sealed is best of course) you can easily store some leaf for close to 2 years. At that point though, the THC inside will begin to break down.