Mesorah - questions that bother a reader

Dear Rabbi,

I like to read your blog and I also use your sefer Das Torah. I would like to ask you a few questions that bother me. They are about our Mesorah.

1) How do we know that the Mesora is True 

 The Rishonim (like Kuzari) bring down the idea of Transmission. And they say that it could not be that millions of people were deceived, and that for sure since they all saw it and heard it, they transmitted it as they saw it and heard it. But what if there was a certain (one or few) person in a certain time (when they were together as a tribe of certain people) that told to their people and convinced them to believe that this is what happened, millions of people were there, and "we got the Torah, and here it is". Like it happened in other religions - one man convincing many people to believe in something, all the more so if people in those times were very receptive to believes of different ideas of religion (for example they were very easily  lured into Avoyda Zora) and obviously (at least for me) since they were not on the same level of rational thinking as in later times (in times of Gaonim, Rishonim or our time). So how we are so convinced that the Mesorah is true?

 2) Accepting that the whole Torah was written by Moshe - except last 8 verses

Another question that bothers me is the assertion "that the Torah is written completely by Moshe Rabeinu", and the only argument is about the last eight psukim. One Tana said that Yehoshua wrote them, and Rabbi Yehoshua (I think it was Rabbi Yehoshua?) said -  "Chas v'sholom,  of course Moshe Rabeinu wrote the whole Torah, just last pesukim he wrote with his tears". But why should I believe in what Rabbi Yehoshua said? At least if he would say that it was his Mesora that Moshe wrote the whole Torah, but Rabbi Yehoshua did not say that. He just based his Pshat on the fact that it is written “that Moshe wrote all this Torah”, which in simple meaning does not prove anything - the words “all this Torah” could simply mean all the commandments. Why should I believe in something that came from human mind as his idea? And all the more so, why should I believe in what he said about this concept, when I know that many Rabbis had the intention of protecting the Torah from heretics, which is very good, but since their minds were constantly in the "protecting mode", they automatically thought in this direction - that of course Moshe wrote the whole Torah, what else is possible?! But as it seems to me, there are many places in the Torah where it seems as if the Torah was not written by one person at one time, but it is more like a collection of a few writings that were put together later on. (For example גיד הנשה - “בראשית לב:לג "על כן לא יאכלו בני ישראל את גיד הנשה", or another place - בראשית לו:לא "ואלה המלכים אשר מלכו בארץ אדום לפני מלך לבני ישראל" , and there are many other places that are indicating this.) I understand that this idea is very dangerous, but the truth is more important to me. I grew up in a communists country, with a mindset of being anti-religion, and even thought I am Shomer Torah umitzvos now, I still have this attitude that everything has to make sense, and for me “this Rabbi said this and this Rabbi said that" is like the Pope in church said this and this and this, and everybody answers “oh yes father, whatever you say”. This way of thinking absolutely foreign to me and I only accept something if it makes sense. Of course I understand that a human brain cannot comprehend everything - but that's as long as it is something that it is not possible to understand, for example בחירה. But if something looks that it is possible to understand logically, why shouldn't I attempt to do that  - to the best of my ability? And then when we don't understand, we use Emuna. And that being said, I don't see anything wrong with the idea that Moshe did not write the whole Torah, like Rabbi Yehoshua holds, since it is his personal opinion, and not the mesora, (at least it does not say that). And it is not perfectly logical to say that Moshe wrote the whole Torah, because of all of those allusions to it, like I wrote before. So basically my question to you is - what's wrong with my understanding, since I don't find any Orthodox Rabbi that holds like this? (only conservative) Or maybe this logic is correct, but Orthodox Rabbis would never accept this because it is too dangerous?

Please answer me, if you can. I specifically chose you because of your rational approach to things.

Thank you,