Something catchy first...it's the only one the festival organisers will listen to. The meat in the middle. I prefer to finish mine with something of the sailing-off-into-the-sunlight type, some prefer upbeat. I dont think it matters that much by the end, maybe, It's the first 2/3 that count.
    If a track is difficult to fit in anywhere, chuck it out. Either it's crap, or it might go well in your next CD. Either way, it won't do in this one. CDs definitely dont need padding. They can be as long as you like. Certain people moan at anything short of 74min...they think they are being ripped off: ignore them.Length is not everything.