Wow...well if you are going to go about creating Napoleonic dios not yet having acquired much knowledge on this period, you have your work cut out for you.
In TS world, I think WWII probably do more volume sales than Naps, despite the overwhelming enthusiasm of Naps collectors. But unlike so many military conflicts represented in TSs, which cover a relatively short period, the Napoleonic campaigns span a 20 year period and involve 8 major powers and a lot of smaller ones. Uniforms, cavalry furniture, and tactics evolved considerably throughout this period, and each nation could be characterized by the formations you might see according to the date and battle represented.
So what do I like about Napoleon? Beating him mostly...I have a lot of British troops, and Britain lost no major battles in the Peninsula campaign, and of course, you know how Waterloo turned out.
A few collectors here have mentioned the variety and vividness of the uniforms, and I agree, but I will add the range of types of troops and the variety you get from changing uniform codes throughout this period (including flag designs).
If you are creating a diorama for this period, you really have to know the specifics of the date and battle. You cannot, for instance, simply transplant troops meant for a Waterloo diorama onto one for Corunna (6 years earlier).
And that is the joy of Naps collecting and dio building, learning the fascinating and complex history over this 20 year period.
Good luck!