I'm sorry I don't want to be rude..
But it seems that you have no idea what this video gear is about...
I think you can better find somebody that can advice and help you setup your system locally. Who can help you setup the camera's the right way. Install your mixer and get everything in working order.
I don't know where you life? But maybe you can consult a BMD dealer or installer. They can give you advice on site and help you to get the right gear for the job.
HDMI is for 10 meters maximum! Otherwise you need a converter. HDMI > SDI
For the JVC's you need a converter Analog > SDI (connect it with component cable not composite.)
BNC cable is standard video cable used in professional setups.
The converters I talk about can be found here>
http://www.blackmagicdesign.com/product ... rs/models/The BNC cable is something you make tailor-made. Look at RG-59 video cables. And use BNC connectors to the end.