Re: Bokken, Jo, Sword?
I have studied Kashima no Tachi with Inaba sensei for quite some time. He encourages practicing with a live blade as you need to work carefully. It also challenges you and requires a strong tanden. Working with an iaito can teach you bad habits - a shinken keeps you honest.
In terms of actual instruction I had only a few hours direct teaching, before working with my own shinken and taking the time to "get comfortable" with it and with practice (primarily battojutsu). That said, I had lots of training on tanden and working in fairly intensive way with bokken previously - it really helps.
Note that Inaba sensei is big on safety. It's about judging when someone is ready to do it, but it doesn't take long to get them going subsequently. And they can learn a lot on their own (as long as they don't act stupidly!)