I think Dave answered all of your questions regarding the cable length.
I can give you some feedback on your antenna and mount as I'm running that same setup on my 40. I put the mount in the location of the OEM antenna on the drivers side of the cowl. I had to add a support (regular i
-bolt) above it to keep the antenna from moving too much because the mount was threatening to crack. It works really well there and looks good I think.
You can sort of see it in this picture: