James, my 2 cents, being an engineer I would suggest you rely on some expert advise from those who design these systems or you can get into trouble fast. Case in point is the pressure required. I agree with a previous reply that you need something with higher pressure capability than a vane pump. The water depth alone will require 9 psi to get the air to the bottom. And your correct that your line needs to be sized correctly or you'll add a bunch more resistance. If you use 1 inch line 1000 feet long and assuming about 10 cfm from pump you would lose another 2 psi (more if higher cfm). That means just to get the air to the diffusers you'll need 11 psi, not accounting for check valves, diffusers, and losses in elbows or bends in pipe. This tells me that if your source is suggesting a vane pump with 1 inch line they are cutting it pretty close. Find a better source. Here's a web site that has data on pressure loss in pipe and fittings for reference.
http://www.aquatext.com/tables/frict-air.htm#CFM%20and%20PSI%20%20Table. I'm not sure I agree with the poster who states that the membrane diffusers are more efficient. I haven't seen one that is more efficient than air stones at dissolving air into the water. There is a world of difference read this (http://www.aquaticeco.com/index.cfm/fuseaction/popup.techTalkDetail/ttid/49). But he is correct that they are relatively maintenance free. Just keep in mind that in order to get the same amount of air dissolved into the water you will need more cfm which can tranlate into 3 times more power and higher electic bills. I would argue that for a large lake you really want to maximize efficiency. Over the long run this might far outweigh the occasional replacement of air stones. Air stone life depends on your water chemistry and whether you have a good air filter. Also read this about membrane versus air stones, also give some good advice on cleaning.(http://www.aquaticeco.com/index.cfm/fuseaction/popup.techTalkDetail/ttid/78)
