After fixed numbers of Players dicovers specific numbers of blueprints for that single item - its getting UN!blocked for all other players to craft. (knowledge gots spread thru world)
1. So, the ability to craft such item gets
UN!blocked for all players (when it reaches certain quantity), - players will still be able to find blueprints. - YES
BPs don't get blocked. - YES
Or is it that those who are the fastest in finding them will be the only ones who are able to craft and then expensively sell these items? - NO
But only those who has Blueprints can benefit from crafting that item with a chance for crafting statistic bonuses.
2. Umm, is the BP then needed when you're on workbench? - NO
Or once you use it, that item is forever in your fixboy? - YES
You "consume" it, and after that u can craft this item with bonuses.
Just one more thing: will you tell us the minimum efficient Trap skill for removing those bear traps and explosives around containers? Will tools maybe give a %bonus to disarming them (i.e. to the trap skill)?
Something around 80 traps should be totally enough, + expanded lockpick set and u should be good to go.