My friend swears that RAI, ALL cantrips can be cast as a bonus action!

How/when would Elemenal Affinity bonus apply in these 3 cases?

So do you need a focus to cast spells with only verbal and somatic components?

Do both weapons need to be light to gain the bonus attack?

War Caster feat: Booming Blade as a reaction to enemy provoking at 5′ -> 10′, is a reach weapon valid for the melee weapon attack?

Kuo-Toa scepter: should I allow the 4d6 lightning damage?