Yours in an interesting case.
Considering you being a Hindu and the girl being a Muslim, your case would be covered under Special Marriage Act, however, you have not mentioned if you registered your marriage with the registrar or not? Also I'm not sure if the ceremonies were witnessed and any certificate was issued to both of you?
Now coming to your questions, assuming that your performed a valid ceremony and duely registered the same, see below::
Q1.) How long it will take in our case to get divorced.
A1.) As you already mentioned that you are living seperately from your wife for more than one year and certainly there has been no co-habitation, you can directly file a petition for divorce on grounds of incompalibility or certain other valid ground as per Special Marriage Act. The court would after hearing both of you may accept your petition. Then you have to move another application after 6months and the court may pronounce a divorce decree. So this way it would take 6-8 months after you file divorce on mutual understanding. Please ensure that no one retracts on your petition in the second motion application as it would be fatal for your case and court might not allow divorce.
Q2.) can i file divorce in mumbai
A2.) You can file divorce only in the local family court where you got your marriage registered. If you married in Delhi, and registered it in Delhi, then you could only take divorce in Delhi and NOT in mumbai.
Q3.) How much visits does we both have to go to the court.
A3.) Already answered in A1.
Q4.) will our parents will be asked by court to come in. Though they are aware and they want also want to end this relationship with mutual consent.
A4. No. Parents are not required. But yes. You never know what the may think to reconcil you guys. He may ask the parents once so that he can explore the possibility of continuing the marriage. But chances of a judge calling parents unnecessarily are scant.
Q5.) What could be the approximate expenditure i would have to do.
A5.) It depends on the lawer. In my view, any lawer in this case should not charge more than 10K as the lawyer would only need to draft two petitions and visit only twice with you. Maximum he may have to visit thrice if the judge is on leave or similar circumstances.
Q6.) Please suggest me a advocate in mumbai. You can leave the contact number or email id and i will contact you back.
A6.) I'm from Delhi. So I could only suggest an advocate from Delhi. If you need one let me know