In modern Japanese one would say 何本も何本も.
- 幾 is indeed pronounced いく.
- The 本 (ほん) following it just appears because the 柱 are counted with 本.
- The doubling is for emphasis.
幾本も
pole after pole
幾本も幾本も
pole after pole after pole
In modern Japanese one would say 何本も何本も.
幾本も
pole after pole
幾本も幾本も
pole after pole after pole