What kind of cheerios did you get? I don't find them sweet at all - actually, a little bit salty. I don't think there is much sugar in them, if you get the plain kind. If you're afraid of dd choking, you can wet the cheerios a bit with some water or formula. I did that with ds when I first gave him cheerios (also paranoid about choking here), but after two days, I just gave them to him dry and he was fine. They soften in your mouth quite quickly.
As for peas and corn, I've read that you should smush peas slightly so that they're not round anymore, but I've never done that for ds. He seems to mush them up quite well himself. Corn, on the other hand, I don't even know if he chews or not because I find kernels in his diaper. Heh. But the outer coating can be quite tough so you might want to mash them too. Oh, and fresh corn is much softer/easier than frozen.