[RPG] the scale of the map of Rokugan

Here's the big version of one of the maps you linked to. Zoom in to 100% resolution and you'll see the scale in the bottom right of the image: 1 hex = 65 miles.

This map was included with the D&D 3rd Edition Living Greyhawk Gazetteer, so it's about as official as any source you're going to find. Note that the political boundaries represent the world as it looks like after the classic modules.

This high-detail fan-made map by Anna B. Meyer also comes with a scale at the top of the legend on the right side. (It's available in multiple versions: with no grid, with a 12-mile hex grid, and with a 30-mile hex grid.)

Since I am really involved in D&D 3.0 and 3.5 I can answer your question but you will not like my answer; In-Setting differences between L5R and D&D in general have so many setting differences that you could write a 3 book novel about it.

The big ones: In D&D your gods are different and thus how the world came to be is much different as is the lore behind your setting, In Oriental Adventures you have the world of Faerun all around you and it can influence your campaign in ways that might change it largely outside your theme of "L5R". Since the Oriental Adventures takes part around the territory of Thay and the Great Dales from the Unapproachable East as in most D&D Faerun based worlds.

BUT this is not the case in your campaign because you are choosing to use the Oriental Adventures custom version of the L5R lore in Rokugan, which by default lends directly to L5R The history of Rokugan;

*

Encompassing more than a thousand years. The last forty or so of those years are of particular interest, since that is the time period covered by the Legend of the Five Rings card game and novels. This chapter cannot hope to describe the events of the Clan Wars, the War Against the Shadow, and the Spirit Wars in any kind of exhaustive detail. A summary of key events in those years appears here, and each clan description below gives a current snapshot of the clan, with details of the most important events leading up to the present.

*Page 207 of the Oriental Adventures book.

As far as I can read their should be no difference in setting between the L5R series and the D&D 3.0 or 3.5 Game you wish to run unless you specifically change something to form fit your game or world. The differences you mention above about people eating meat is simply an observation that can be over ruled by any GM, also the way to the dragon homelands is completely up to you as the GM to build and thus could easily mirror exactly as it dose in L5R.