What is the ruling on someone who doesn`t perform prayer?

All perfect praise be to Allah,The Lord of The Worlds                                                                                                                                                                    Not performing prayer is a major sin, and one who doesn`t pray out of laziness is considered an oft-sinner ;whereas, the one who denies that it is mandatory is considered a disbeliever. And Allah Knows Best.

What is the ruling on a suitor (khāṭib) going out alone with his fiancée before the marriage contract is concluded?

It is unlawful for a suitor, prior to the marriage contract , to do anything that would be unlawful for any non-maḥram man — including touching his fiancée, being secluded with her (khalwah), or seeing her without her complete sharī‘ah-compliant covering — even after the recitation of al-Fātiḥah (This is a cultural custom to seek Allah's blessing (barakah) and mark mutual consent) and the family's approval [of the engagement]. This is because the engagement, without the formal marriage contract, does not render unlawful matters permissible. And Allah, the Exalted, knows best.

Is Zakah (obligatory charity) due on the money saved for marriage?

Zakah is due on the money saved for marriage if it reached the Nissab (minimum amount liable for Zakah), and a whole lunar year had lapsed over possessing it.

Is it permissible for women to gather in one of their homes to pray Tarawih?