We've been there for one month while working remotely on our laptops. The WiFi connection is really good and covers whole apartment without any issues. I recommend to take external keyboard for your laptop in case you will be there working for longer time period as it allows you to put the laptop on higher place on the working table which is more comfortable.
The equipment in the apartment contains everything which you usually need and in case you are missing something, the owner is willing to lend it to you.
The apartment offers 3 rooms in total, first one has window facing to the street and doors as well, second room does not have any windows or doors, third has doors and window which opens just to the hallway, but this is quite usual on canary islands from what we heard.