Number 1 - Yes.
Number 2, bthen don't get the tree or the stats, just get an ability outright. This is sort of the expected result. Good with thief escorts at the least, and even on some of the others. Precognition has saved my life, multiple times. Arcane eye is inordinately helpful, and so can premonition, though that one might be expensive for a mana using class like shadowblade.
Then there's the light tree, which every magic based class can make GREAT use of. But even failing that, the basic healing light is a great heal spell for a shadowblade, or any mage class.
3 - Go for stuns. Every character needs stuns.
Currently playing under the name Aura of the Dawn 4 down, 227 to go!
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DarkGod has two arms, one with an opened hand, one with a closed fist. You got the fist.