I've done all your questions and the answer is yes
You can use everything and anything in one project, the key being lots of everything to make it one. Just one or two magentas for instance will stand out like a sore thumb, use whatever you are using through the whole quilt.
I've also found breaking it down from that, leaving out all the red and black makes a better cohesiveness.
My favorite though is combiningg all one color, from lime and seafoam to spruce...a richness that can't be matched in commercial matched up color lines.
If you google string quilts, you'll be consumed with ideas and plans
Sharyn