[You really should have started a new thread for this discussion, which is heading a long was from the Subject line, and is a good discussion in itself]
Jaffa don't have pouches - so what. They can still be "troops", just not with larval Goa'uld. Ra was the first to use human hosts - maybe he's a traditionalist who doesn't think the symbiotes should be sullied by being "raised" inside humans.
Ra race was dying - if you were portraying a god you'd probably be a little secretive about saying "actually there's an entire planet of people like me" since that sort of demeans your status as god. BUT, the race could be dying: if for some reason the Unas race (later in SG-1 suggested was the first host species) was no longer suitable (perhaps due to the addition of naquadah in the blood to control ribbon device etc) then the race COULD be dying
Ra is not human - he's never said to be!! In fact, the opposite. Ra was not human but took on human form as host. And that clearly IS true.
Sam is in the movie - where? Her own character says she isn't, in "COTG". Although your reference only applies to the US DVD but I think I've tracked down the relevant bit: there are two blondish haired woman in the control room during the first dialling; SO WHAT? They aren't played by Amanda Tapping, and none are credited as Ms. Carter; indeed one is credited as "Jenny". Just because they're young, blonde and female doesn't make them Cpt Carter. Heck, you could say the beared bloke that Daniel steals the marker from to draw Earth glyph on the monitor is Robert Rothman...
The ribbon device IS very slightly different in design - this could just be due to it being an "older model" BUT it's used ENTIRELY consistently later in SG-1: it has two modes: the "throw the victim across the room" and "torture to death". These are both seen in throne room when Ra dealks with the offendig Jaffa; they are both seen in SG-1 episodes: Apophis throws some of SG-1 in "Children of the Gods", Sam does similar in "Seth", etc (ad nauseam); Klorel tortures Daniel (again!) in "Within the Serpents Lair", Amuanet tortures Daniel (yet again!!!) in "Forever in a Day"
Helmets - perhaps; Ra is just arrogant...
Others you've probably noticed: one of the biggest is "that's right - it's on the other side of the known universe" when talking about Abydos, when in COTG Sam says "it's probably the closest planet in the network to Earth"....
At the end of the day, we just have to either "explain" the differences or gloss over them. The series has to have a consistent mythology and technology for itself, which MAY have to be different from the speicific design concepts of an inherently self-contained movie which wasn't designed to be making such things for a 7-8 season series ...