Those sound like good enough guidelines for me... one to two session adventures, SRD material only. Encounter levels, recommended PC levels, difficulty, and everything else is up to the entrant. I think we have enough info to get started!
Actually, one opinion query: though restricted to SRD (or MSRD) materials only, does that mean we cannot include new, original mechanics? I always like to throw a little extra spice into my work, so odds are any submission from me will include some original crunch alongside the scenario. Can we agree that producing original mechanics is okay, or shall we leave it at just the System Reference Documents and nothing more?