(2) Who is a wali of girl?
بسم الله الرحمن الرحيم
(1) Dawat-e-Walimah (post-marital feast) should be arranged by groom. If nikah is solemnized in the day and walimah is arranged in the night then too it is alright. However, it is better to arrange walimah the next day after husband and wife meet first time in privacy i.e. nuptial night.
(2) The Wali of the girl is her father or grandfather or brother etc from asabat (blood relations) lines.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.