Lumpy is fine I tend to lose some of that when I strain it. Also they used to keep this stuff in a goat stomach bag and the tradition was hit the bag every time you walked past it so it's ok to give it a shake.

Using long life milk sounds almost like heresy to me. Perhaps they suggest that incase people get the ratio of milk to kefir grains so out of balance it goes off before it ferments?!

I try to to keep the type of milk I am using as similar as possible. Just be wary of any fresh milk not coming in contact with the grains or curd as it could go off, hence why it's worth giving the container a clean every so often.