eos and selene serve different purposes

you'll want to use eos for more healing intensive fights, whereas selene can help more on dps races

besides their 3 unique skills, eos and selene are the same, their respective embraces heal for the same

bane only spreads bio, bio 2 and miasma (and it only spreads to 3 other targets, the tooltip is incorrect in that regard)

i usually shadow flare, bio2, miasma, bio, and then bane (followed by a miasma 2 if i'm bored)
edit: you can multi dot thunder and aero if you want to though i usually don't

neither adloquium nor succor will stack