If possible, I recommend finding a dojo where you can learn kendo...receiving formal instruction is important, especially at beginner level (that applies to all martial arts). I think it's best to have a teacher in disciplines that might cause physical injury if improperly applied / learned. Nevertheless, training alone isn't impossible, it's just harder and riskier in my opinion. Also, from personal experience, since I've always been interested in swordsmanship but didn't have the chance to learn it from somewhere, I practiced some things alone, from descriptions or videos. I started doing suburi (the basic move in kendo) with a suburito (that's like a short, thick stick used for doing suburi, and much heavier than a normal shinai or bokken), and also tried to imitate what I've seen in a dojo that I've visited. But I thought..starting gradually is boring, why don't I do 1000 every day? So I did...until after a few weeks I had to stop because of an injury, which ironically, is common in kendo, especially if your technique when doing suburi is wrong. So if you do start training alone, I advise to go for steady, gradual progress, to minimize the risk of injury.
About Musashi and the other swordsmen who learned by themselves, they are an example that it can be done. However, those times were different, and samurai as dedicated as Musashi probably spent their whole time just training and thinking about the sword, and testing things out. Those were days when their survival depended on their skills..in our age we can't dedicate that much time to training with a weapon that is no longer used in combat, so our progress wouldn't be as good as theirs.
The KendoWorld forums and youtube channel are a good place to start informing yourself about kendo. Also, I've found the youtube channel of a Japanese sensei called Hiro Imafuji quite helpful and easy to understand for a beginner.
And by the way, kendo is a more modern version of Japanese swordsmanship, and it's not exactly what the samurai used in combat, which was referred as kenjutsu. Musashi's Ni-Ten Ichi Ryu and other styles are all forms of kenjutsu. Kendo evolved from that to become what it is today.
