To send letters you can use the post in Garbejaire, see map below. The good thing is that you do not need to wait in the queue, but just use the machine on the left side. It has both scales to weight your package and touchscreen interface to specify destination. You don't even need change - there is machine that will exchange your bills.
General
All the advice that does not fall into the other categories.

This is a nice surprise. If you don't have your own laptop, you're not lost yet. You might get one for free from the university. Of course you need to give it back after the academic year. You also need to give a financial guaranty for it. Still if you need it - go for it.