Kojima has said that he doesn't want to remake MG1 or 2 because he would have to rewrite large parts of them and he doesn't really want to do that, so I'm thinking that's why he wrote in the connections that V has to them. The Metal Gears in the first two games are different, and made by Dr. Madnar. However, Rex from MGS1 looks to have the same head so it's not inconceivable that the Patriots/US Army would have used parts of Huey's (well, Granin's) design. I do think you have to take a lot of MG1 and 2 plot points and how they fit in with a grain of salt, being that Kojima never expected to make anything other than MG1, let alone all that he has up to now.
That said, as MG2 goes, I would call the 4th ending canon because it fits in with the opening story of "the Cold War has thawed and the threat of nuclear war is a thing of the past". Also, we don't know how long it took. It may have taken into the mid 90's in game time to disarm all of those. I did love all the nods to the Boss (Joy) in the ending on the monument and from Big Boss.
We've been playing through the other games in the series as well and it's pretty interesting to see some of the links that you would pay no mind to without playing V. For instance, Granin compares his Metal Gear to the missing link and sells/gives the plans to Huey, who builds Sahelanthropus, which is also called the missing link. Nothing that changes the story overall in a huge way, but really helps to tie things together and build on the lore.
I loved the voiced acting too. I didn't like Miller's character so much on a personal level, with all of his whiny incredulity, but Downes did a fine job with him. Skull face was just awesome. There are a handful of silly or hammy lines from them both, like Miller and his hamburgers, or this gem from Skull Face
, but I think that adds a lot to the feel and spirit of the game.
As far as Quiet and BB/Venom goes, there are a lot of people who would postulate that she was going to kill Ishmael, knowing he was BB. Ahab was the "patient in the next bed who saw her face". Given that, it's entirely possible she knows all the time (at least after the assassination attempt and being captured) that he isn't the real Big Boss. I'm not sure whether any of that was the intent of the writers, but it's something to think about.