Too much work! I'll just stick to my unanswered/interesting questions.
SPOILERS OBVIOUSLY
I'll say it again:
LOADS OF SPOILERS IN THIS POST!
Okay, to make it a bit easier to read, I'm going to pull all the questions off quote.
These answers are based on my understanding of the story. I don't have anything to back it up. Feel free to correct me if I'm wrong
1) Did anyone else have any trouble hearing the dialogue? Esp. the Japanese guy, Saito.
Not really. Well, he's got a Japanese accent, so it might be a bit difficult to comprehend. But I was also reading subtitles at the same time, so maybe that helped

Also, I think the Forger had a British accent? Maybe that's why he was a bit difficult to understand.
4) Was the first dream within a dream a test by Saito? I thought they were hired by rivals of Saito, but then I read later when I got home it was all a test set up by him. If so, who was chasing Cobb when he went to meet with the Forger, Eames?
No, the team was hired by Saito's rivals (COBOL group, who were seen chasing them later on), but Saito had had some prior training in protecting his dream, and Mal showing up messed things up, so the mission failed. However, Saito saw their talent and wanted to use it, so he hired them.
5) Am I right that any of the team can alter the dream? Cobb did this subconsciously, but I don't know if this was a rare problem, or if anyone could do it. I assume that the car and guns aren't put there by the architect, hence the line (I heard it!) about dreaming "a bigger gun". Basically, why'd they have a dream machine on the third level? They weren't expecting to go any deeper.
I think so, but here is what I think:
The Dreamer: serves as the 'canvas' in each layer and holds the dream in that layer together (therefore cannot leave their layer, or the dream collapses)
The Architect: designs all layers (and is free to travel through the layers)
The Subject: populates the dream with subconscious projections
The Forger: impersonates someone the Subject knows to get secrets
Other people: just players who can move around
I agree with ReflecttcelfeR that you don't want to alter the reality in the dream too much (like pulling guns out from nowhere), because it alerts the Subject's subconscious that it is a dream.
About the dream machine, I thought they could always have spares, you know, in case one breaks
6) Speaking of the dream machine, why do they need it in the dreams other than to fool Fischer? It's all imaginary at that point, why not just take the red pill? Or maybe it was the blue pill...
My understanding is, with a new layer of dream (dream within a dream), the first-layer dream becomes 'the reality'. This is why when the car falls off the bridge the second-layer dream also goes zero-g. However, why this effect doesn't reach the third layer is beyond me. Perhaps physical effects (gravity, water, etc.) reach only the layer directly beneath it?
7) If they can alter the dream, why don't they do it more often? I'd think a bullet-proof Iron Man suit would come in handy. Why couldn't anyone do what the Forger did? Did that require talent, training?
Like what ReflecttcelfeR has said. Once the subject knows they are dreaming, the mission is over.
8) Speaking of conjuring things, was anyone else disappointed by Limbo/Cobb's id? Architecture is great and all, but wouldn't a subconscious have Godzilla stomping thru or something? He was able to dream up his kids and wife. Hardly any sign of life otherwise. I was expecting something more trippy like Eternal Sunshine.
I expected it to be worst, with the name limbo. The thing is, I don't think it's a very pleasant place and I can imagine that just falling into it must feel like crap already. So I suppose that's the best they could do.
11) I saw OMW came to the same conclusion I did - does it really matter whether Cobb's life is but a dream or not? Does it matter to you?
This is a very interesting question! Strangely, I asked myself and for me I don't care if it's got a 'happy ending' or not. He faced Mal. He faced his guilt, his grief. To me, the whole thing feels
resolved already.
But I swear the thing was really slowing down at the end! I like it how it ended like that. You know everyone in the cinema was staring at that thing
12) Of course a lot of the above doesn't matter if it's all a dream. I didn't ask myself most of these questions until after, much like you don't question dream logic until you wake up. Was that all on purpose by Nolan?
It's all a dream? Er.. that never occurred to me. But if it were, then what's the point?
This brings up another question(s) about Limbo: how does one escape? Must it be willing? Why didn't Cobb just kill his wife and himself and wake up? Why bother with inception in the first place? How did Eames know when to use the defib on Fischer? Why didn't Fischer go to his own little Limbo area instead of Cobb's? Saito did.
You escape by knowing you are in a dream and killing yourself. However, I think when Cobb and Mal were trapped in there the first time it was by accident. You only go to limbo when you get killed in a dream and can't wake up (e.g. you're sedated). So, getting killed in limbo won't do anything, because your body still cannot wake up. The only way is to wait it out until the drug wears off. However, Mal was going crazy so Cobb had to convince her they were living in the reality.
Saito didn't go to his own limbo area. The beach was the same place that Cobb and Mal dreamed up (you know, right at the beginning when Cobb washed ashore and got picked up by Saito's men). I think they said it somewhere that limbo is built up from collective subconsciousness (or something like that), so everyone in there gets to create a little bit of it.
Interesting take on the totems! I'll have to think more about it.