I would just concentrate on the focal lengths that you like rather than 'best' lenses. For example I have the 90mm f2 as well, and it's a nice lens but ultimately it's one of my least used lenses. I use the 50-140 and 56 way more for the portrait your shots I see you post. The 16mm is also a good lens, but I just don't use that focal length so have never bothered with it.
What is it that you want to shoot? It's good advice to use your existing lens at 16mm to see if that works for you before dropping the cash on the prime. It seems a bit of a leap considering the type of shot you normally post in here.
Then again, this is photography, where does logic really come into it when buying new gear, fill your boots