Is every Orthodox ordination, in and of itself, valid?
Where on the spectrum I described is Orthodoxy?
uh, both. "the act of ordination itself causes ordination to happen" and "the validity of the ordination is not so much in the individual but in the Lord" are both correct statements (though I'd make the second stronger by removing the qualifier: "the validity of the ordination is not in the individual but in the Lord").
Does ordination cause a permanent change in the character of the ordained?
No. The ordination, like any other sacrament, makes certain Grace available to the ordained (from the actual service: 'Divine grace, which heals every infirmity and supplies every deficiency, elevates' X to the presbytry/episcopate). It does not remove his free will and thus his ability to reject that Grace's activity on his own soul.
Can an ordinand lose his ordination, or he a priest forever? Likewise a bishop?
Yes. What the Church bestows it can remove. A priest or bishop can be deposed (returned to the laity) by a canonical judgment for immoral/uncanonical behavior.
Does Orthodoxy emphasis a strong division between the laity and the clergy, where the role of the one is principally to be obedient to the second?
Not sure you can get an objective response, but my subjective perspective would be no.
Where does authentic authority in Orthodoxy lie? Who can call an ecumenical council, and have there been any since the 7th Ecumenical Council?
Authority rests only in the Church as a whole. Even a general council is only recognized as ecumenical when it is received by the Church. Second part there's no real answer--all the historical councils were called by the emperor but that had more to do with him having the logistical/practical ability to gather that many bishops than anything else. Should today's bishops ever overcome all the logistical hurdles to hold the much-discussed General council and said council's decisions are in accord with the received Tradition then it may be recognized in retrospect as an authentic ecumenical council. Or to put it another way, in one sense, no one has authority to call an ecumenical council--such councils are only truly recognized in retrospect by the consensus of the Church (see, for example, the 2nd Ecumenical Council).
And in that sense, yes, the second Photian council (the one that reinstated St. Photius and affirmed his teaching) and the hesychast councils which affirmed St. Gregory Palamas teachings on Grace are often considered Ecumenical Councils--although, frankly, Orthodoxy doesn't get too tied up in the terminology. What's important is not if we count them as 8, 9, etc but that we recognize them as authoritative statements of the Church's teaching
If an Orthodox lay person reads in his Bible that sheep are blue, and the Church teaches that they are actually yellow, must he at the peril of his salvation admit that they are indeed yellow, and that his perception must be wrong?
Impossible to answer. Since if the Bible says that sheep are blue then the Church says that sheep are blue. On the other hand, if he thinks the Bible says such a thing, and the Church points out that it does not, in fact, say any such thing, he would be foolish (and prideful) to hold to his interpretation over that of the consensus of the Fathers.
On the other hand, the Church actually has a relatively small number of things on which it has spoken that you *must* believe this (those would be the decisions of the councils). In general, you can be wrong and it not imperil your salvation. To take two real examples (as opposed to blue sheep):
1) If a person reads about Joshua and the sun standing still and therefore insists that the Sun revolves around the earth, he is wrong. The Church would say that he is misinterpreting Scripture and try to explain the difference between literal and figurative, narrative and authorial perspective vs. objective reality, etc. But it doesn't inherently imperil his soul. He may be a fool, but he's still Orthodox.
2) The Church clearly teaches the assumption of the Virgin's body into heaven after her death. We have a whole feast dedicated to it, canonical icons of the event, and the hymns and prayers we all sing on that day are clear on what happened. But Orthodoxy doesn't say you *have* to believe it. The disposition of the Theotokos's earthly body isn't particularly relevent to your personal salvation so you are free to believe what you want, it won't 'imperil your soul' (although in many cases, the pride which causes you to set your own judgment over that of the Fathers is probably imperilling your soul--but the belief itself is not the problem).