1/ Location doesn’t matter, iPhone/Android use neither.
2/ Do not exceed 80-100 DMs per day to your own followers. You should aim for 50-60 at first glance, and see if you can do more later on. Always increase slowly.
I would say start with 15-20 DMs a day and then increase it slowly if you notice that it’s going fine and that you’re hitting the limits. I think you should be safe if you’ve got only those two accounts logged from the same device.