I think if anything will happen the rootfs will be enough, but I wouldn't know.

For meego you need an external sd, sure. Even if you could install meego to the emmc there would be no point since you can't have access to your device. And, No external sd didn't come with the device, but they are cheap now. You can get one for about 15? or something, and then you will have an extra 4gb of storage. Meego requires class 6 for speed but since you want it only for a specific one-time use, I can confirm it can boot off of a class 4 too. It's painfully slow, but you'll do your job
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Colorado Dispensary