Purity of x max resist and increased effect of buffs on you / increased aura effect

A rather simple question: do nodes mentioned in topic affect the "+ max resistance" bonus from purity of fire/ice/lightning?

Also, if the answer to previous question is "yes", than, just out of curiosity: ara the two types of buffs cumulative? To clarify: let's say a person runs a level 20 purity of ice (giving +4 max cold resist naturally), and also has +20% effect of buffs and +5% increased effect of auras. Will he/she get an additional point of max resistance?

auras are buffs
"increased" modifiers are allways additive

Thanks for the clarification (it means "yes" to both, AFAIU).

Regarding additivity: I realise that they are additive, and "more" are multiplicative, but wasn't sure about rounding issues with different types of additive bonuses. It could have gone both ways, as usually it doesn't really matter (For damage scales of 60% increased lightning damage and 40% elemental, with base values around 250, it doesn't matter that much whether additive bonuses of different types are rounded first, added second or vice versa).

yes

they are summed up into one multiplier = applied at the same time -> no rounding issues from having different applicable "increased" modifiers