Decon 3 is by far the best thing you can have, becuase one stuff up and this thing can undo it.
Dont bother with 1 or 2, level 3 is much more cost effective (you get back more vs what it cost to make it)
you need vigour catalyst 2 in order to remove gums so you can put gums on, add the boons, then remove the gums to put different boons on. In addition using quirk boon gives back extra vigour when using vigour catalyst.
The pastes are less needed, but its pretty damn hard to forge top tier without them. If your still learning to forge however you can forgo them for now.
Reading my guide might help you get a better idea.