I didn't get a chance to make some comments about your service.
The issue of different accounts of the resurrection appearances, even apparently irreconcilable, is actually a strength of the evidence of something happening after Jesus' death, not a weakness. An analogy is with an accident. The police will say that if everyone around an accident gives the same account of what happened, something is wrong. Validity comes when there are all varied accounts from which pictures of what happened can begin. Another aspect also said to give strength is that at the time women were inadequate witnesses, and yet are are at the tomb when empty. The issue here is that if the writers wanted to convince readers about an event which did not happen, why then put women as the first witnesses? Of course this may equally be a hint that it did not happen and it is a later tradition.
So I disagree with the thrust of your point that the evidence suggests it did not happen, because the evidence suggests something (but what?) did happen. I would go further to say that a problem with Unitarian accounts of Easter is that they do not tackle the resurrection appearances, and how it is that the disciples who ran away then came to proclaim a faith in Christ as risen. I would give some answers but I do it along with Christians rather than dismissing the evidence of some after-impact. My conclusions would fit with the radical theologians who do tackle Easter.
I would also say that your statement that people of other religions would agree Jesus is the greatest man who lived is not so. There is no way that a Muslim will speak of Jesus in this way set against Muhammad, or the Sikh compared with any of the ten Gurus. Hindus might be generous but Krishna and Rama make more sense in their richness. The reason is because of how much what we discuss of Jesus is based around faith, both of the people of the time and since. There is not a neutral humanist Jesus who impresses because this is also a faith product. Just as he was not original in terms of the Law and coming Kingdom of God, nor is he particularly unique as an ethical man. There is not a ranking system at which Jesus comes top - there is no way of knowing.
As for Jesus' witness because of AD and BC, it is becoming more common practice now to use CE and BCE with the same year numbers. I have never used AD and BC in Religious Education lessons, and nor should anyone in any school in or out of RE. Yes we know that Christendom (not large numbers of followers) created a calendar based on an estimate of Jesus' birth, but this is not how it is used now, and there are other calendars too.
I noticed you separated out issues of God from Jesus. The question becomes, if Jesus is so demonstrative, even as a heroic faith figure, does this mean there is more of God (in whom you believe realistically) in him than in anyone else? I think Martineau's statement about incarnation more broadly is in the end a cop out, because Unitarian views like his (the broader wing at the time) actually made God distant and disconnected. There were good reasons then why God should be (attachment to a supernatural Jesus). The incarnation however is an attempt to root a real human life and God together. For me, the usefulness of incarnation as a language of faith has to be in eating a meal, drinking, taking a walk, meeting other people, developing community.
And, finally (you'll be glad to know) the prayer you began with grated a bit, regarding the Unitarian church as a haven away from bigoted religion. I did see a BBC 4 TV programme recently, all Anglicans, discussing of all things the resurrection, and it was not at all bigoted, and I'd just suggest that mostly religions are about holiness and spirituality, and working things out, and nor is bigotry exempted from Unitarian circles. It should be, but it is not.