@thomas-heiss I tried the English for German speakers course. This time I did get all of the first 12 correct so it did give me the placement test. It still tested me out of ~1400 words, which I largely put down to one typo and a couple of cases where it didn't accept a synonym of the word it was looking for. So the placement test is working, albeit imperfectly.
I've already completed the German course and decided to start the Spanish course. Unlike with the German course, I was not given a placement test. It has just started me off with the very easy words, which is very annoying as I do already know some Spanish (even if it is getting a bit rusty).
Here some thoughts of mine on points 1 and 3, although note that I studied German rather than French but I presume the courses are set up similarly.
In my experience, if you get a word correct first time round, it never asks you for that word again. So that's essentially the same as telling it that you definitely know that word. I also found that after spending a lot of time on the course, I suddenly got a lot of really easy words that I must have skipped because of the placement test so you do still get tested on whether you actually know the words that were skipped. Although I was given a lot at once, and I think it would have been better to mix them with the harder words.
I highly recommend setting up your keyboard to 'English (International AltGr dead keys)', which makes it very easy to type accents and suchlike in any program, at least for romance and germanic languages.