Your activity should not have much of an effect on other users, however I would not recommend updating the initial information through wifi, you will be there forever. I think you would be safe for now, for there are not to many people looking to hack public wifi bitcoin access, just my opinion though.
Thanks for the warning. I'm considering using a dead mobile as offline storage. Dead as in without a network connection of course.
There is nothing to hack, the data is verified locally if its modified it will be discarded. If I wanted to get hold of a bitcoin wallet I would not sit at a McD for a week either. Its more likely that you are targeted in general over a public WiFi (e.g. your Windows) than a targeted attack on full nodes. Finding full nodes is easy online, why go to a place where the chance is smaller than finding a block with a CPU?