A couple of quick points here since I have done the research on german hefes and have dispensed Erdinger and Schneider Weiss in my kegerator successfully.
In general, it's not that difficult once you accept the fact that the beer was intended to have an extremely high CO2 content level. This was designed by the brew master. Your looking at around 6.8 grams/liter as a max CO2 level. I forget my conversions from g/l to vol of CO2 (I actually did all the calcs at one point), but it's in the neighborhood of 3.2 - 3.3 vol CO2. Yeah, that high.
So, if you go straight CO2, at 38 degrees, you're looking at a pressure of ~ 19 PSI. It is also true that if you go that high with 100% CO2, the beer will overcarbonate in about a week or so. I go with a 60% CO2 and 40%N blend. If you go with a blend, you will need to increase your pressure significantly to balance the co2 content or the beer will eventually go flat. You can find more information from McDantim's website (
http://www.mcdantim.com/brochures.htm). With a blend and the right PSI, my german hefe kegs last about 1-1.5 months. I can't say enough about the folks at McDantim. They know their stuff and the website is extremely helpful.
So, where does that leave you for line length? It's 2.2 lbs/ft of restriction for 3/16" vinyl tubing at a flow rate of 128oz/min (industry standard). Therefore, at 19 PSI, you're looking at 8.6 feet. I typically go with a slightly longer run to slow the pour rate down a bit.
If you go by those general principles, you will have no problem dispensing a german hefe.