I find the Nikkors I own or have owned better than the zuikos(28/2,8, 50/1,8, 135/3,5) I had some years ago.
20 AFD 2,8 is a great superwide lens
28 Ais 2,8 is very good for closeups (20cm limit). Parted with it by mistake.
50 AFD 1,4 beats anything except
the 85 AFD 1,4 the best lens I have ever owned.
180 Ais 2,8 ED a great tele but on the FE (or FM) the motordrive is required for the balance.
Bjørn Rørslett has a great site on the Nikkors
http://www.naturfotograf.com/index2.html
I had a Sigma 24 mm f/2,8 lens, the old version and that focallenght is very usefull. Not as difficult as the 20mm and not as boring as the 28mm in generel use. It went to 18cm And it was when I sold that one I got the 28mm, I love to move in very close with wide angles. I also had the Sigma 105mm Makro but in the end I found it not good enough, somehow it lacked something. I never got a Mikronikkor instead though
If I was to start over again today with a FM and a 105mm I'd probably go out and get the 50mm f/1,8 and the 28mm f/2,8 for closeups or the 28mm f/2.0 for general use. (cheap, semi cheap solution) and then perhaps get the 85mm f/1,4 (very expensive)
Another option as you mentioned is to sell the 105 and get the 35mm and 85mm f/1,4 (more expensive solution)
Cheers Søren