OK, First question:
I don't use head cement, havem't in years
Second question:
dry flies & nymphs=down eye
spinners=up eye
any fly smaller then 26 I use a straight eye
Third question:
using over sized hackle will cause your fly to stand on end or not float properly, also I blocks the hook point.
lastly:
don't get hung up with exact patterns, tie flies with what you have to match the flies hatching, often the ugliest flies catch the most fish.