Agree with MWN. It's also pretty typical. Coaches always promise the moon when they are trying to build the team...I learned the lesson the hard way the first year and that all the talk about being a family and promises like State Cup and trips to France were nonsense. He may not have a choice, BTW, if it's a new team and the record did not sustain placement in flight 1, depending on the league of course.
The flights don't really matter at that age, particularly to a keeper. The flight 1s are just kids that are early bloomers and can run really fast. The coach obviously is mindful of the morale and doesn't want the team to get blown out the entire season. The flights are supposed to be about making sure teams don't blow each other out, but they've achieved a weird status symbol thing which is distorting soccer (as you can see from the other thread of the guy complaining about his flight 1 bench players).
The three things you say that might have me a little wary. One, that the coach seems to have had the ambition to have pushed such a young team into flight 1 so early. It may be he's one of the types that cares more about the wins than the players development. Two that he got upset at you guys for missing a week (at that age, it's expected you'll miss weeks....it may be though he's putting too much reliance and pressure on your keeper in which case your keeper might be the scape goat if they lose [happened to us the first year]). And three because he's placing a lot of reliance on your keeper, that at such a young age he doesn't have a substitute and your child is playing between the sticks the entire time. Particularly if the coach doesn't play the back pass and allow your child to always take goalkicks, without field practice, your child may not develop the footskills he needs to be a modern day keeper. See how it goes and how he uses your keeper this season, and if you aren't happy, change next year...that's how it goes with keepers (they change around a lot as their needs and skills and challenges change).