If I relied solely on Kurso de Esperanto to learn Esperanto, and completed all 12 levels, how proficient would my Esperanto be? Beginner? Intermediate? Advanced? Fluent? I'm aware that fluency requires continuous practice with other Esperantists, but I'm hoping to be intermediate after Kurso de Esperanto. Would I then be able to complete Lernu's intermediate courses? Or even the advanced courses?
I have been using the beginner Lernu courses to learn but I need a break from it so have decided to try Kurso de Esperanto.

In my opinion “Kurso de Esperanto” is one of the best Esperanto courses available for beginners online. I learned Esperanto just by completing that course. After completing the course, you won’t really need to complete other more advanced courses, just try to extend your vocabulary and to get a feeling for the language by using it (here in the lernu! forum for example).

Although I did not use Kurso de Esperanto, but rather the book Teach Yourself Esperanto, I am self taught and can confirm that you can definitely reach fluency from a course like that. The key is to listen to spoken Esperanto, and to try to write as much as possible (and have someone correct your grammar). Speaking fluently will come with time.
PS: where in RSA are you?

I did the entire Kurso de Esperanto course and the best way I can put it is that it leaves you as an advanced beginner. My reading ability is probably intermediate'ish' but with writing and speaking I'm still awful.

Thanks for pointing this course out. Since I read this thread, I have downloaded it and, since then, have almost completed it. It's a good course and an excellent place to start. I, too, started with lernu.net and with that and a few side trips (I've used "The Esperanto Teacher", also) I have passed the basic level exam. Kurso de Esperanto didn't really teach me a lot of new stuff, but there was been some stuff that has become clearer, and of course, it's all good practice. I can recommend it.

However, a reality check may be in order. A quick search on the Internet makes me think that most languages have hundreds of thousands of words. Kurso de Esperanto introduces maybe forty of so in each of it's twelve lessons. I did the lessons pretty quickly since much of it was review for me, but had I been starting from zero, I reckon that each lesson might have taken a few hours, so that I could maybe complete the whole thing in, say, 50 hours. Esperanto might be easier to learn than a national language, but it's still a pretty major undertaking. I certainly wouldn't expect to be able to reach intermediate level in 50 hours.

To be more encouraging, let me say that, for a free course and 50 hours of work, being a beginner with some important concepts learned is pretty good. Also you will, of course, be able to complete Lernu's intermediate courses after Kurso de Esperanto. But you probably won't breeze through them. And you will be able to reach intermediate level after Kurso de Esperanto, too. Just not immediately after.

Well it's a little off topic, but I think they could improve Kurso by turning it into a web site. HTML5 is more than capable of reproducing the functionality of the application. This would enable the course to reach a wider audience range, especially if the site was mobile responsive.

I would also like to see something similar to Lang8's functionality in the site, ie encouraging public writing and community correction.