Just check the specs on stock singlespeed bikes
Most stock singlespeeds run 32*20. You can use the gear calculator at Sheldonbrown.com to see what the equivalent ratios may be.
I'm running 34*21, which is a tad taller, but I wish I went shorter. I thought 32*20 was perfect for my level of fitness (not very good) and my terrain (hilly, but I tend to avoid the big hills).
I also recently switched form 175mm cranks to 180s. I hardly notice the loss of 'spin' but I love the extra bit of torque. BTW, I'm 5'10" with a 33" pant inseam.
Also, I think the EMD9 does not have any kind of chain adjustment. You either have to find a 'magic ratio' (which doesn't account for drivetrain wear anyway) or use a tensioner.... and IMO tensioners suck. I ran a Surly Singulator on my old singlespeed, and could not get it to keep my chain from jumping. Push-up, push-down, locked down however... didn't make much difference.