1) Could have easily been covered up as a massive terrorist attack by an unnamed source and those who witnessed it be passed off as crazies. Since there was no communications active at the time no one would be able to send any information or such, making it easy to round up any visual records of the fight.
2) As pointed out, they needed parts to repair Megs, but none of the bot's would be sacrificed so coldly. Plus from the time Prime died to the time they met up in the desert, Sam was no where near them. He was evacuated and hidden away before Prime could be safely recovered.
3) While somewhat of a plot hole, I chalk the mystery 6th bot up to being Blackout, the chopper, being brought back to life. He was dead near megs too and it's possible he was rebuilt as well. It would explain why he appeared right after Megs came back and followed him and Starscream around.
4) Ignoring the accent bit, as Transformers have always had some accents, you don't need to wear glasses because you have poor eye sight. It could have easily been an external scanner or simple magnification device. Plus, it was pretty damn cool.
5) Pretenders, Transformers disguised as humans/organic beings, is an old G1 concept. So the idea is certainly not new, but the execution was. And who said metal robots had to be heavy? Frenzy was made of metal but could be carried effortlessly by a stewardess. Different compositions for different functions.
6) This one is difficult to actually answer unless you start delving into TF lore, which is foggy at best. Especially concerning the movie-verse.
7 and 8 are spot on though
9) Sam was, for all intents and purposes, connected to the Allspark already. Through that connection, and his efforts to willingly sacrifice his life to save those of others, on the brink of death he had a vision. Something a lot of people claim to have on the brink of death. It's just that his was of Prime's past, who saw his deeds and rewarded him justly.
10) Mikaela, we watch her wrap his hand. Trapped in a pocket dimension iirc, I think this was explained in the comics. Satellite's bounce tons of info from one to the other, Soundwave found the right one, attached himself too it and controlled it to be able to gather info from all other satellites. Bad humor. Worse humor. Some say Decepticon protoforms who scanned similar alt modes, I say bad directing and a cheap way to get more bots in the film. Because the Government are dicks and think the only reason why there is fighting is because the Autobots are there. Because ancient, primitive humans saw this giant construct of unknown origins and worshiped it, building a pyramid to protect it from outsiders. G1 Homage? As he says with a screenshot of Mikaela's nice white pants covered in dirt sitting next to his comments.