In this detailed fatwa Mufti Abdul Qaiyyum (حفظه الله) of Jamea Islamia Dabhel, Gujrat, India, has proven the permissibility of raising funds through lunches, dinners and barbecues etc. He explains that different methods for raising funds were used in the era of the Messenger. He also shows how the Akabir of Deoband employed innovated methods of raising funds for Islamic purposes. He dispels the notion that using this method constitutes emulating the Non-Muslims by explaining what constitutes tashabbuh bil kuffar and what does not. The doubt that some cast on the intentions of the donors has also been dealt with.

He concludes that people should partake in such events without any qualms or reservations.
Yes, there should not be any intermingling of sexes at these events. That would be prohibited.

This fatwa was endorsed by the last of our elders, Hazrat Sultanul Aarifeen, Muhaddith Kabir, Faqeehuz Zamaan, Murabbi Jalil, Mufti Ahmed Khanpuri (May Allah preserve him and allow us to benefit from his presence). Hazrat Mufti Abbas Bismillah (حفظه الله)  has also endorsed this fatwa.

Mahmoodul Fatawa Vol.5 Pg.286-604
See the 19 page detailed Urdu Fatwa here.