You're on the right track I think. Its easier to scale back at first, and build as you go, than the other way around. Keep it light, while maintaining comfort features. After even a few nights, you'll have a much clearer understanding of your own priorities. (cooking, sleeping, plumbing, floor, temp control, light, power, layout, etc.) I think storage should come last, as its easy to have portable storage first (boxes come in all sizes and shapes!) Your wall space is limited, so you'll want to use it wisely, preferably the first time.
You're already half-way there with insulation, A/C, windows, and electrical! Keep us posted with pictures.
