Evil/Embrace Dark Urge Questions

Hello everyone

I've been trying to complete an evil playthrough with the Dark Urge but I'm a bit worried about messing something up and it taking forever to go back. I want to do this playthrough "right" in a way.
Mainly, I was thinking of killing every companion before the final battle to stand alone in my triumph (I know you mostly stand alone anyway but I think it's cooler if I kill them all before)

I don't want to spoil myself on the ending to embracing the urge but I want to know if I'm making the right choices to get the "ideal" evil ending.
So my questions are:
-Are there any companions I should absolutely spare?
-Who should I romance (if at all)? I'm not a big fan of romancing companions since I'm not a "romance" kinda guy but then again I'm not a "murder innocent people" kinda guy either so I might as well try to romance whoever would make the playthrough more fun. I was thinking Astarion since I've heard he turns you into a vampire spawn if he ascends.
-Are there any characters I should hold off on killing for a bit?
-When I get to act 3, at what point would it be ideal to go on a rampage and slaughter everyone in the city?

I know these are really weird questions but any help would be appreciated