I run mine at about 35psi and have my keezer set to 37 degrees. Try serving at pressures between 30-40psi to see what works best for you. I have found that higher serving pressures yield less foam. 20 psi yields about three fingers of head for me. This is somewhat counter-intuitive, but others I have spoken to also report this phenomenon.
Make sure that your beer is carbonated to the appropriate volume before you evaluate your pour. Some just hook up to the beer gas and let it set at serving pressure for about a week. I hook my nitro bound kegs up to CO2 at serving pressure for about an hour before hooking up to the beer gas. I typically see good pours within a couple days with this method. A word of advice: DO NOT OVER CARBONATE! Your beer will taste funny and will not pour well. It is better to under carb and wait than overcarb and have to start over.
As so your line length, I run about 7ft for mine. However, a stout faucet contains a restricter plate within that the tap that may make line length irrelevant. This plate is responsible for the cascading head. I think it knocks the gas out suspension? Either way, the stout tap is ultimately responsible for the total restriction of the system so you need not be concerned with the line length in terms of the restriction factor.
Finally, don't be afraid to experiment with all types of beer on your nitro tap. Don't have a stout ready? Toss your keg awaiting the traditional tap on the nitro! I'm currently drinking an IPA from my nitro tap and its like a delicious hop milkshake.