I experienced the course as interesting and in no way strenuous. The rituals are based on a set of basic techniques which you learn early in the course and they are not "difficult" per se, and they are handy to work with later.
If you like reading in the evening, you will be gladly spending an hour or so on some weeknights, reading the gwersi and doing the exercises - however, if you are very busy, the course might go slower. I took about 18 months to finish and some take longer. You can choose your own pace. Actually the pace is one aspect I liked in the course. At the end of the year, you will have roughly 500 pages of information. If you just went out and bought a 500 page book, and gobble it all up in a couple weeks, you would not get a fraction out of it.
No, you don't "pass or fail". You and your tutor determine when you have "finished" the grade. Your tutor may suggest that you work with some material again if they feel it is necessary and beneficial for you. I can't repeat often enough that the tutor can be the best part of the package
I can't really comment on whether the other grades are less "self-directed", perhaps a druid grade member can help us out here. On calling yourself a druid, that is up to you - do you consider "druidry" a religion, or do you consider "druid" a title? I would not call myself a druid even if I had completed 19 years of training, but that is a personal decision.
If you are a voracious reader you will probably read books on the side, so there may be some duplicate information. You won't get bored with the course, I would guess, unless you are extremely demanding
Check out the reading room for book reviews!
Perhaps you have seen that you can try the introductory package first, to get a feel for it, before embarking on the full course. You can also keep hanging out here and see what some of the members "are like" and how "we do it" - so welcome on board!