Lots of stuff here. I'm sorry I didn't come back last night. Not too well, back on antibiotics. Joy.
Will endeavour to address some points - not sure I'll get to them all 
And do you really believe that 40 years of people passing on stories they've heard to each other is likely to result in a consistent & reliable account? No one, out of those hundreds and hundreds of thousands of people would have over egged the pudding? Made a mistake? Lied to make it sound more exciting or convince their loved ones? Stories were passed from country to country, language to language - no mistranslations, no misunderstandings? That the story began in this way does not favour your case, it does exactly the opposite. We already know how useless we humans are when it comes to detail - ask any police officer. This is, essentially, a game of Chinese Whispers played with hundreds and hundreds of thousands of people. The results when you've got 10 kids sitting in a circle is comical enough - what do you get when you widen the circle that considerably?
40 years is not a long time. In our times, 1973 is very clear in memory. Now, it is easy to say that is because of modern media etc, but the oral tradition was the main way of communication in the first century in this culture, and, as I have said above, cannot be compared in any way to a game of Chinese Whispers. People learned great chunks of scripture completely verbatim - hard to get our heads round how this could be possible, but it was done, and likewise the accounts handed down were learned. They were not passed down in scraps and vague memories, or in whispers whereby the listeners were not sure what they had heard - there were checks made at every level and tellers would be brought up on inconsistencies. Added to that was the fact that the gospel accounts were at the most second hand, if not more (will be going into this later) and therefore there was no way in which things could be changed to the degree you are suggesting.
I don?t know how you?ve concluded when Luke converted to Christianity, there?s no indication of when that was that I can find.
I didn't say Luke had converted, I was talking about Paul. Some of the passages show how Christians had consolidated their beliefs and practises very early on and how they had even formed early creeds. This was in the time of eyewitnesses, both those who followed Jesus and more hostile witnesses, yet this thing grew and the central claims remained unchallenged by those living at the time and generations soon after.
And Luke as a witness is not particularly valuable, given that he was copying most of his information from other sources, mainly Mark & Matthew - and he was also guilty of making up important information (the fake census came from Luke).
Hmmm. I'm not sure the fact that Luke may have used Mark and others for source material can be used as a charge that he as a witness was not particularly valuable. There's plenty of extra material in Luke, and as for the census, there's another thing altogether, maybe something we can talk about in a while.
No, it?s not a myth, and I?m really surprised that you would say that. All of the books of the NT have been subject to considerable amounts of mistranslations, mistakes, forged passages, interpolations, deliberate & accidental textual changes etc etc. This is without question and the result is that there are more differences between all the copies that we have than there are words in the entire New Testament - they run into the hundreds of thousands.
I think I used the word myth because I hear this argument quoted so often from people who have not studied anything of this and believe what they hear. I am not in any way saying that this applies to you - I admire your knowledge and know you have studied in a great deal of depth. It does therefore surprise me a little that you think that the NT has been changed around enough to ensure that it cannot be used as historically viable material. A good amount of scholars do not think this is the case.
Let's take the differences that 'run into hundreds of thousands', for example. This number is very misleading. The way differences are counted means that if one word is spelled incorrectly in, say, 3,000 manuscripts, this is then counted as 3,000 variants. It is easy to see how the variants can build up to a seemingly huge number when you take factors like this into account.
It's also worth noting that no actual doctrinal statements are variated, even in these thousands of 'mistakes'. No central tenets are changed. And if we are talking about the changes between the gospels, I think I said something earlier about this - that no central material differed between them - that the differences were secondary points, according to audience, theological interpretation, linguistic device etc etc. I have compared the gospels in parallel, as you suggest, and far from finding too many variants as to make the whole thing untenable, I am struck again and again how much consistency there is, as well as finding the different 'takes' fascinating. I don't find the differences a stumbling block, but do think it is important to examine them and look to why they may be so.