on question 1 it's 7.5 give or take a little, so 7.9 sounds fine. the "7.5" cell should be front and the 11" rear for your 7.5 focal length
on 2 the front cell is your 14" cell. Always best to put it behind the shutter when shooting
you should put your 11" cell behind the shutter when using it alone as well. Don't worry too much about distances from shutter to film plane with the single cells. Use the gear scales on the bed when setting up, and it should work okay. Do you have gear scales on the bed? Kodak usually set the cameras up pretty well. Thes are formulas for setting up gears floating around the net somewhere.
25 gears is a huge amount. The cameras came with 8-10 gears for a triple convertible lense. Camera usually had three to 5 fans, three being the most common. They should be marked with the shutter speed on them