Forgiveness for sins

Q: If we had committed any sin in the past and we are not sure if it was a sin, should we ask any Mufti or Aalim regarding that thing or just repent from all sins and move on in life believing Allah has forgiven us?

Validity of nikaah if spouses don't perform salaah

Q: If a man and woman love each other but don't engage in haraam, both are Muslim, believe in Allah Ta'ala, the prophets, Quraan as Allah's book etc. but don't pray BUT know it is obligatory, will their nikaah be valid? Will their nikaah be void?

As I have heard that such couples nikaah is not valid if they don't pray before marriage, don't pray up until marriage and after marriage.