They did mention the screw size in the guide here by color coding the MM. I agree with point two, but that's nitpicking. Lastly (the reason I commented), you did it right. The plastic should be removed so it is just like the orig battery, if you would leave the cellophane on, the adhesive would be stuck to it instead of the battery and making for a poorly secured battery.
Overall, the parts and kit were good, but this phone is not my favorite iPhone to work on. Getting that old battery out was extremely annoying compared to the 4, 4s, 5, and 5s that I've all done in the past.
On a side note, this is the first ifixit branded battery I've received and I've ordered a lot of parts from them over the years. They used to source what looked line 100% orig batteries. I avoid non original batteries like the plague, I don't care if it's a phone, laptop, or even my APC UPS devices. Ifixit has earned my trust over the years with all the parts and tools so I went ahead and installed it, I'm sure it's good.