This guide explores some of the nuances of the system for a DM looking to create an adventure in the East Marches. For any questions that aren't addressed here, feel free to ask any of the other experienced DMs.
Basic Guidelines for an Adventure
The two most important things that an East Marches adventure needs to be are short and self-contained.
Each adventure should be no more than a single session, or perhaps two, and should range in length from 2 to 6 hours of playtime. This way both you and your players can play and not have to worry about scheduling handfuls of sessions across any number of time zones. Obviously, being up front with the overall time commitment, especially for longer-length sessions, is important.
Each adventure should also be self contained. It should be an adventure with a clear beginning and end, and a clear goal or target. All involved characters must be returned to the airship at the end of the adventure and, as such, cannot be stranded in another plane or other inaccessible location.
How many characters? What level?
You, as the DM, can design an adventure for any number of characters. Want to run an adventure for a pair of people? Go for it! Want to run one for a relative horde of eight? Sounds like hell, but make it happen. Just make sure you factor in that every character added has the potential to slow down your session (and make things harder to manage and balance overall)
You can also set a level range for your adventure, but it should be for a range of levels that currently exist in the guild. The range can be as large or as small as you like, but a smaller range is recommended due to ease of balance. All characters within the adventure will level up at the same rate.
Where can I set it?
In a word: anywhere. The world is a blank slate. Create a new town, forest, mountain range, or dungeon; or piggyback off of features created in a previous adventure to give the world a more lived-in feel. You can host multiple adventures in the same locale or the same town if you wish.
Can I use lore, locations, and NPCs created by another DM?
That's one of the major points of this. Yes, you may. Once an adventure is completed, it's essentially canon for the world. Any NPC or location encountered or every piece of lore learned is part of the world for the future.
As a courtesy, though, I would recommended talking to the original creator of whatever you plan to use before making any major changes to it (like destroying a location or killing/turning an NPC) both to make sure it fits with what they might have originally viewed and to ensure that you're not taking something that's already involved in that DM's future plans.
What can the adventure be?
Essentially, an adventure can be whatever you or your players want it to be. A dungeon crawl, an assassination mission, a monster hunt, a daring heist - all are possible assignments in the adventurer's guild and each might draw out a different cast of characters that believe they have what it takes to satisfy that mission.
Can I adapt an existing module into East Marches?
The two most common DM commandments I've read are "make sure everyone has fun" and "if you aren't stealing, you aren't DMing." Steal what you want. Borrow what you want. Adapt what you want. Just try to make it your own and ensure that it fits in the East Marches world.
How do I handle loot?
To keep things consistent between adventures and ensure that all characters can progress on relatively even footing, there will be loot rules in effect that will scale based on the level range of the adventure. These loot rules will establish a base sum of gold to be awarded on completion and an allowance for gold, loot, and magic items that can be found or acquired during the course of the adventure.
Can I run a multi-part adventure?
Sure, why the hell not? If you want to run a series of adventures with an over-arching story, you can do so, provided you give the opportunity for the party to return to the airship and restock or reshuffle the roster. I would avoid anything too long, as that's not the point of the East Marches campaign.
How do I create an adventure in Kanka?
Make use of DM Info - Creating an Adventure