Jan van Leyden
Adventurer
2 adventure paths a year. Each set in a different setting. One is an old, classic setting, one is a new setting. Each takes characters up to about 20th level and are designed for 6months to a year's play. Most DMs will buy one a year.
Each AP has a shortish setting guide which introduces it and adds any specific character options. Not too long - you want to hand this to players and expect them to look at it.
What about DM information? Would you like it implemented in the adventure itself, i.e., the town where part of the adventure takes place, is outlined or described in that part of the adventure? And new monsters, will they only appear in the relevant sections? This style should make the adventures much largerand expensive, wouldn't it?