I have played strictly frost for the past 3 Xpacs and want to try out Unholy. But i took a look at all their spells and talents and im unclear on what does what exactly. Could i get some help with spell rotation and talents to take for maximum PVE damage? Both ST and AOE?
The rotation you want to follow is: Maintaining Virulent Plague with Outbreak. Spending runic power with Death Coil (offense) or Death Strike (defense) only when you can regain runes with Runic Corruption or if you’re full on runic power and need to spend some so you don’t waste your runes. And use Festering Strike to apply Festering wounds and Scourge strike to pop them. Use a couple Festering Strikes before using Apocalypse (one of your burst cool-downs that also pops wounds) if necessary. and use Dark Transformation pretty much whenever possible.
As for talents: ST would be 1.) All Will Serve, 2.) Ebon Fever, 3.) whatever, 4.) Soul Reaper, 5.) whatever, 6.) not really a ST talent row so meh none are really all that good they would interrupt ST rotation, 7.) Unholy Frenzy.
AOE Rotation is a bit different: after applying Festering wounds drop a death and decay and spam Scourge Strike, the rest stays the same. As for AOE Talents: 1.) Infected Claws, 2.) Bursting Sores, 3.) whatever, 4.) Pestilent Pustules or Soul Reaper, 5.) whatever, 6.) Pestilence or Defile, 7.) Unholy Frenzy
To be honest I’m not sure about Unholy rotation anymore. I just faceroll it and still doing good damage 
I would 100% run epidemic for AoE. I made an M+ guide if you wanna look at rotations in AoE. It’s for 8.1.5 but o it essences have been added since. https://youtu.be/wqT5ND-Dazo