Craft mats - couple of questions

Hi Community
I have a couple of questions regarding crafting materials. Prolly both dumb , but going on the only dumb questions are those never asked ......

1) The gear dismantler
I have these legendary materials and I don't seem to be able to craft anything with the craft shops I have , nor do I seem to be able to find any crafting recipes ?? is there some special place I am missing either to craft or buy recipes ?

2) Halloween craft mats

I got a lot of stuff left over - sell or keep ?

Thanks in advance