Runewords should go more in D2 direction.
Runewords should span across legendary and ancient legendary in power scale. Low easy runewords for mid-game is great aswell, like for exemple a stealth or ral ort tal shield i believe it was. Spirit was a bit too powerful in regards to which runes it needed.
2. Very important. As u said. It makes white and eth items and sockets interesting. Not just salvage or crap u dont pickup. Runewords was great although some were too overpowered. So runewords should be similar to legendaries its just a different and enjoyable Journey and crafting experience..
And finally, dont give us the exakt list. Let the players find small Clues to try and figure out what runewords exist. Will make launch more interesting