QTR-Quadtone RIP

I have an Epson 2400 and I'm new to this program. Regarding Curve
Creator tool: 

1. Is the lineariaztion function similar to Curves in Photoshop, with
steps in 5% increments?  And does adding to a number (e.g. 0 to 12.23)
darken that specific part of the print, and does increasing the number
lighten that part of the print? 

2. In the Ink Setup tab, it shows 7 inks for my Epson 2400, three
blacks and two each Cyan and Magenta, with the color inks assigned to
"toner" and "toner 2" curves. Is it possible to create a curve where I
turn off the C and M inks (by selecting "not used") and then only use
the three black inks? And if I do, do I need to adjust the densities
and limits to the remaining black inks? Or adjust the toner curves (I
assume no, since I'm not using them anymore)? 

3. And finally, in relation to the above question, can someone give me
a layperson's explanation of what the density and limit selections do? 

Best, David.