You should be able to do 3000 dps to a target dummy without using curse of elements. 4800 in a fully caster supported 25 man raid.
The rest of the information can be found in the "Fix my dps" thread. Look at what they are asking, what they provide, and how people respond. You will get all the information you need to answer the rest of your questions.
destro, with your hit rating, take the 3 pts in suppression, you need it.
hit rating even with suppression is 289, but that is with a 3% spell hit buff(boomkin or S-priest)
Speaking destro here. Hit>SP>haste, crit and spirit is good, but normally don'T stack them.
get rid of hit gem in priority, pure SP gem is the best atm, unless you need to activate your meta(need 2 blue) or there is a good socket bonus.