It is a pity that you are not completely satisfied with your stay. In my opinion you smell the smoke of the downstairs neighbor only in the hall and it is perfectly fine behind the door to the apartment.
As far as Wi-Fi is concerned, that works fine for the normal use of internet and apps, but not for the work you do and where you have to download and upload large files. From the guests we have received we have no complaints about the wifi. It is also useful for yourself to buy a better internet connection, because you can take it to your new home in Leiden, but for normal internet use the wifi in the house is fine.
Following your stay and the noise pollution below , caused by a running child, we have decided to install a new floor, so that problem is solved next week. In addition, we have in the house rules noticed that it is an upstairs apartment and that you have to think about the neighbors . With old houses like in Leiden there is more inconvenience than in new houses.
I hope the other apartment will please you for the rest of your stay.