--DO I HAVE TO SPEAK JAPANESE?--
One issue to keep in mind when considering either the bus or helicopter tours, is finding one that will accept foreigners that can't speak the language — if that is an issue in your case. Language is one of the toughest questions when discussing the pilgrimage. When asked if you have to speak Japanese, i have to offer a qualified "No, not really."
While i can't personally imagine attempting it without being able to speak at least a minimal amount of survival Japanese, i know people who have successfully walked the pilgrimage and who tell me they speak virtually nothing of the language.
For the convenience of non-Japanese speakers, i am building a small English/Japanese vocabulary list that may help you to communicate with non-English speaking Japanese. Words and partial phrases are written side-by-side in both English and Japanese. By pointing at an English word/phrase that you can read, the Japanese speaker will see the same word/phrase in Japanese, which they can read. The list doesn't contain any sentences (for that you should buy a phrase book), but by pointing at various words and prases on the list, and stringing them together one after the other while the Japanese person watches what you point to, you should be able to construct short, and incredibly disjointed, but understandable, sentences. If you use it, please let me know if you see ways to improve it, or words that you think should be added.
The difficult part of the trip for non-Japanese speakers will be reserving a room each night at one of the minshuku. One person told me that he simply asked the owner of the minshuku he was staying at one night to call the next night's minshuku and make the reservation for him. If you get a friend who speaks the language to make your first night's reservation, that should have you home free. Another alternative is to skip the minshuku and the reservations and camp out the whole time. Then all you have to deal with are restaurants, grocery stores, and rain.
Because of the language barrier Japan could be one of the hardest countries around to travel in. But, it is doable. It is doable and enjoyable with the minimum survival vocabulary and a large sense of humor. The people of Shikoku are wonderful and will go out of their way to help you out when you need it.