OK, I will give my impression
If, I mean if I really get enough money to build Mordor fortress outpost
(1) Morgul. its orcs are more sustainable in the battlefield, that's important for Mordor to maintain the front line.
(2) If possible, witchking is always more attractive but that's not important factors
(3) I guess, I mean I do not have many opportunities to recruit their elite units anyway
(4) I think they are balanced, Morgul orcs are more defensive while Dol Guldor orcs could poison their enemy in long run
(5) Damn too high
(6) None of them, the other buildings have more urgent need, I don't need free spiders and I don't understand the influence on Morgul fortress
(7) The regular orcs are definitely more powerful than original orcs, Morgul riders are good supplement for Mordor but they couldn't be recruited in early game, when Mordor needs fast units badly.Dol Guldor stewards are effective based on my limited experiences
(8) Spiders, have no place for them
(9) Yes they are, I strongly suggest a system like laketown or Dale, a basic building costing 1000 first, then upgrading different buildings(orcs barracks, witchking shrine etc) for recruitment of different units or defense or economy boost, not they cost 3000, and are have no defense at all. It would be better if they could enable regular Mordor barracks to recruit corresponding orcs units somehow, just like 3.8.1