1) Before 2.1 I only used Perfect Balance as a "recovery" skill for if I lost GL3 (like heart phase of titan or other "jumps" on primals, etc.), generally not as an opener, because I would risk pulling hate if I used PB right at the start. Tank threat is better after 2.1 so I use it as an opener a lot more. PB > Demo+Snap2x || Snap3x > DK > Twin Snakes > PB wears off, start normal rotation to ensure GL3 doesn't fall off > DK/BS > True Strike > Demo || Snap > ToD > etc. Save your cooldowns like IR and BfB for after you get GL3 up.

2) Proper way to maximize DPS is single target burn them down so the healer can DPS! If there are 3+ enemies I will use Rockbreaker. Depending on movement I may toss DoTs on other targets, but don't do that at the expense of your rotation. You're not a summoner.

3) General rule is you shouldn't have to ask about this because it doesn't really matter. Make it dead and do what you can to not lose GL3.

4) Fracture is alright in fights where you won't go dry. I keep it on my bar but don't use it frequently. I use it on Titan a lot because of so much movement, good for throwing on before moving for bombs and so on.