Assalam o alaikum wr wb,May Allah (swt) be pleased with you all and guide yourselfs and all the Muslims to the right path.My question is 1.Does a Muslim needs to perform the (Nikah) marriage ceremony only in the Masajids or he can perform them at some Function Halls.2.Do we have any sound Hadith relating a marriage ceremony of any Sahabas marriage which was performed in the Masjid.3 Can people of the Brides family may be, her father or her guardian demand a certain amount of Mahr, is this a vaid act.4 If the Mahr what Bride groom can afford is less then is a valid reason for the Bride's people to reject the marriage proposal.Is there a rule regarding this in the Shariah . I am sure you will reply me with Quran and Authentic Hadith .May Allah have mercy on us and All. Wassalm.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

It is not an obligation for a Muslim to celebrate his marriage in the mosque. He may conduct it in any other place that does not involve any religious prohibition, and we do not have any evidence which proves that any companion did so in the mosque. However, some scholars are of the view that it is desirable to conduct the marriage contract in the mosque. For more benefit, please refer to Fatwa 84483.

As regards the dowry, the wife or her guardian may ask for a certain amount of dowry, and may refuse conducting the marriage if the bridegroom refuses to pay that amount. For more benefit, please refer to Fatwa 90124.

Finally, it should be noted that there are many religious texts that encourage minimizing the expenditures of marriage in order to make it blessed. For more benefit, please refer to Fataawa 86016, 87514 and 83092. 

Allaah Knows best.