Do you take scoundrel and sneak? If so how do you utilize your abilities?
1 Scoundrel for Walk in Shadows (take at creation, because it will be a while before you find a vendor who sells the skill book). 2 base Sneak +1 from Cautious trait +2 from gear gets you 5 Sneak.
With the Guerrilla trait, attacking from stealth gives you double damage. Ending your turn in stealth can prevent you from getting attacked.
Do you stealth before a fight and open from stealth?
Depends on the fight. You can open a fight by stealthing and taking a potshot at someone to enter combat, but at later levels that's probably more trouble than it's worth.
Do you restealth during the fight?
Yes; stealth, shoot, repeat until your AP gets low, end turn in stealth if possible. You need to be out of enemies' line-of-sight or stealth will fail.
Are rangers viable without stealth?
Never tried that...I imagine they'd still be ok as long as you keep your weapon up-to-date and use your special arrows wisely. But Guerrilla + Sneak makes their damage much, much better.
How does haste work in general and with rangers specifically
Haste gives you extra AP and movement speed per turn in combat, but only for a short while (2-3 turns). Extra AP = more attacks and movement, which is good. Pretty useful at the right time if you don't have Glass Cannon, less useful without it, I guess.