I think a mana item is core on every build...ekko desperately needs mana regen. I usually use your first build but i build a morello instead of zhonyas
i think lacking mana/mana regen on a cdr build is a recipe for disaster. not to mention i don't personally agree nashors since there is a cd on his passive but it isn't bad
2.
3.
Switch item orders based on need.
CDR AP
Tanky AP
Joxuu's suggestions are probably better but these are my opinions (>^-^)>