Just speaking outta experience, difficulty dynamics is often the hardest, and arguably the MOST controversial issue a designer can face. Why? What you think to be difficult, and what the community thinks as difficult is different. Newbies, pros, ignorant n00bs, or everyday players will undoubtably test your scenario. So, now you're thinking, well, ok...I'll make an ridiculously easy scenario for the n00bs and newbies, a moderate scenario for the everyday Joe, and an insanely hard scenario for the pros. Done, right? Wrong. Not only does your easy scenario have to appease the n00bs and newbies, but only the pros. At this point, your mind is screaming: WTF! How am I gonna make a scenario both easy and challenging at the same time? That, my friend, is where you learn difficulty dynamics, and using the tent method, which allows the player to choose their own difficulty.
BUT it doesn't stop there. Even when the choice is given, critics will still pop out and say ridiculous items, such as " The Easy Level was waaaaaaay too easy. Toughen it up." Or "The Hard Level was IMPOSSIBLE. Tone it down." It's a never-ending battle, that 9 outta 10 cases the designer loses. Sometimes people overlook the simple fact that: Easy is meant to be Easy. Moderate is meant to be Moderate. Hard is meant to be Hard. So don't get disgruntled or discouraged when people give you that crud. As long as you gave the player the choice to choose his level of difficulty, you are good to go.
And...you kinda came in late on the design train. Standards are so much higher today, then in the past years. All in all, I wish you the best of luck on this outstanding piece of work.
EDIT- Here, read this thread about MM, my first successful campaign, it'll help if you are still worried over difficulty/balance.
http://aok.heavengames.com/cgi-bin/aokcgi/display.cgi?action=st&fn=4&tn=34956&f=4,0,0,0&st=0[This message has been edited by MW (edited 03-20-2006 @ 03:28 PM).]