Re: Bokken, Jo, Sword?
I would hazzard a guess that the most popular jo size is the standard for Shinto-Muso Ryu (and therefore Japan Kendo Federation) jodo - approx 127 cm long and a diameter of 24 mm. 27mm and 30 mm diameters are also made, but not as common.
Metal sword? I have never used them. My only advice is: if you absolutely *must* get a metal sword, buy an iaido mogito. But if you're not going to study iai or kenjutsu seriously, I feel the money would be better spent on bokuto and suburito of varying lengths and weights.
There are dozens of members who are much better informed on the subject, but that's my ￥2's worth.