this depends on the skill itself, in general, unless it’s a true dual wield skill (shadow strike as example) then skills only scale with 1h when dual wielding, primarily main hand weapon.
DEE happens to be “special” and has specific relation to hand/weapon interaction, so 60% of the time it will use your main hand, the other 40% you get left hand weapon base dmg DEE, PRM and some devotion skills do not count in off-hand / left-hand weapon damage
yes, conversion is conversion is always applied where it’s used, so if the skill has wd, part of your skill is phys, you have phys conversion, that’s converted just the same.
that depends if it’s global of direct skill conversion; devos are unaffected in terms of scaling or conversion to the skill it’s attached to, it’s merely a trigger.
If it’s global conversion it will apply to maul, if it’s direct skill(dee conversion) it will not
maul proc causes an aoe/“explosion” to happen around player, anything hit by that aoe gets a debuff dot attached to them. It’s the debuff pseudo dot dmg ticking that heals you (and it being a debuff is why it doesn’t stack on same target), the debuff and pseudo dot then is what lasts 5secs