Grade 1 does include all the numbers, but that's only a few of them. It's mostly just easy kanji for easy words, such as car, river, man, woman, red, white, big, small, among others. I don't believe they're grouped in any order except by difficulty - you can probably see that the higher grade kanjis are a lot more complicated than the lower grade ones.

Edit: not sure if you were aware, but the "grade" actually refers to the grade level that Japanese schoolchildren learn these kanji.

The grades relate to school grades I believe. Grade 1 = Kanji Japanese kids learn in 1st grade (age 6-7).
Its basically in the order of easy to hard.
The Kanji at the beginning are easier (with fewer strokes) and are most commonly used. They are also Kanji that are used as parts to make up other more complicated Kanji.