Depends if your doing it for pest control as landowners may want you to continue through summer, or if you wish to let them breed and make more sport for winter then it seems many people are hanging up the nets this month [me included} until september-october time, hope this helps
Marshall towm builders line from B&Q is ok to work with, its spun poly and comes in various colours, although got to agree agouti is where i get my twine and things
Theres no such thing as a bad ferret, only a bad trainer, same goes with lurchers and most domesticated animals, and colour has no bearing on working ability, there all made of the same stuff.
Only my opinion!
I have one from mick dadd, no complaints, i also have the mk3's which work perfect with mk1 box and which i think is the way to go, as when your mk1 box packs up you have the right collars to just switch to a mk3 locator