Nope. There is one situation, and one only, where you can legally "work" while being on an ED visa. And that is if you are doing an internship as part of the education. That would usually be unpaid though, and doesn't apply to any kind of language learning courses.. It does apply to certain bachelors degrees, if teaching related.
my local office usually requires two sets of everything for my visa extension type. One year they asked for 3 sets. So since then I just always have extra of everything with me. Including photos.
Yes.. put it in a dedicated account with no atm card attached. Let it be a bit over too, to account for the unexpected.
For example if you have it connected to your mobile banking app as well as your every day spending account, make sure it's the right one you transfer/pay whatever from each time. Double check.
Well I agree that it's a good idea to just have it there all the time. But you can get away with only having it in the account for two months before applying, and that's it. At most immigration offices.