Strictly speaking, you only need 2 Crafting and 3 Blacksmithing to get to the max of 5. You can get +2 to each from gear (gloves and belt), and Pragmatic trait gives you +1 Crafting.
Tenebrium upgrades depend on Tenebrium skill. You need 3 Tenebrium skill to upgrade a weapon with a Tenebrium bar. Using the book + completing Brandon's quest can get you a bonus of +2 (although it may depend on the order in which you do them - might be a bug).
You lose all of your skills when you respec. You can re-buy most of them from vendors. Unfortunately Dust Devil is only available at character creation, and I believe the Whirlwind skillbook is unique, so you will lose those forever if you respec.
