6 Element Lenses
I agree, skip the 4 element lenses.
Six element lenses include Rodenstock's Rodagon, Schneider's Componon and Componon-S, and Nikon's El Nikkor.
While a Componon is a six element lens, the Componon-S is more recent and a better, general purpose lens.
The Apo lenses, Apo Rodagon, Apo Componon, and if you could ever find one for under $2000 (!), the Apo El-Nikkor, have more than six elements and perform better. But, one would need a glass negative carrier to get the full advantage of these Apo lenses. One can get excellent results with the six element lenses.
Avoid the Apo-Ronar or Apo-Gerogon lenses. They are process lenses and not optimized for enlarging.