The 9 speed cassette wil require 9 speed chain. 8 or less speed will be too wide to fit between the cogs.
Although the crank was probably designed for 7 speed, it shouldn't be a problem.
I once temporarily used an old cottered crank from a 2X5 (to see if 165mm length arms would work better for me) with my 9 speed cassette/chain without issue.
Bio Pace is a Shimano type of elliptical rings.
175MM is the length of the arms.