Hi
You can either Register under "The special Marriage Act 1954," or get married as per religious ritual according to HIndu vedic rites or in the church according to the christian rites, then apply for a certifciate before the municipal office.
it is better to register your marriage under "The special Marriage Act 1954," as you both are from different religious faith.
You can also conduct the ceremonies under both religious rites to get married and apply for a certificate in the Municipal office where the marriage takes place.
If you are registering the marriage Under special marriage act you need to give 30 days notice of intimation before the registrar. This means first you should apply for the marriage and after 30 days you can sign the marriage before the registrar in the presence of 2 witnesses
In Mumbai if you are doing you can apply in Khar Road office of the Marriage registrar, give notice of 30 days and get married. the marriage certificate will be issued immediately after the marriage.
There is a nominal fee to be paid while applying for the registration.
Documents needed are
address proof of the groom and bride(either party should have an address in Mumbai)
ID proof of the parties
Birth certificate or school leaving certificate to show the proof f the age
passport size photographs
two witnesses wit Id proof