Shadowpriest.net has lots of information on general stuff like a rotation, and there are a few shadow priest threads here alread, and even a spreadsheet to help you see your damage with different gear.
Shadow Priest DPS Spreadsheet
Soon SW: Death will have a 12 second cooldown, so you will not be able to spam it even if you wanted too.
You seem to understand what to do, stack +damage and keep casting those DoTs when the expire and rotate in MB and Mindflay.
Use DoTimer to know when you need to recast your DoTs.