Thanks for the great excplanation Chuck!May I be so bold as to add a small comment (actually two, it's "blauw" and not "blau" as you should know very well )?
When making your want list for your 'less ambitious coins, it does no harm to include the targets of your 'more ambitious coins as well.
If you want to trade your Earth Turtle coin (ID 298) only for coins 507 319 320 400 427 428,I think it's a good idea to put these coins also at the beginning of you want lists for other coins (that you will probably not get these for, but you never know).
So instead of:
(E&Cplus3) 294 : 734 735 736 737 738 739 740 741
(E&Cplus3) 298 : 507 319 320 400 427 428
you would get:
(E&Cplus3) 294 : 507 319 320 400 427 428 734 735 736 737 738 739 740 741
(E&Cplus3) 298 : 507 319 320 400 427 428
I hope I have explained what I meant reasonably well. If not, please feel free to clarify (or comment, of course).