Ok for us to answer some of your questions, you need to give us more information - are you getting a Force FX saber converted? Or buying a saber? If so, which saber? That lets us know what options you have available.
I'll explain about the blades:
Midgrade - thin walled blade, more flexible and not as durable as heavy grade. Still very durable and great for dueling, nice and light and very bright.
Heavy grade - thick walled blade, other than that same as midgrade. Much more sturdy, will hold up against VERY hard surfaces and blows, but loses some brightness due to thicker walls.
Ultraedge - this is a middle grade blade as far as durability goes. Apart from that, the only difference is it uses a milky kind of polycarbonate blade which results in a more evenly spread color throughout the blade - distorts the color a slight amount for the most part.
Ultraedge heavy grade - literally just the Ultraedge version of a heavy grade blade. Same milky color to the blade, same color effect, but thicker walled polycarbonate is used so it has the same durability as the regular Heavy grade.
Nero, may I suggest you(or another mod/admin) make this into a topic and sticky it? I think it' would be a good idea. Just a suggestion though.