It is best to do the wedding feast (waleemah) after the marriage is consummated, following the example of the Prophet (blessings and peace of Allah be upon him). But if that is not possible, then there is nothing wrong with doing it before the marriage is consummated, or when the marriage contract is done, or after that.
The matter is broad in scope, but it is better to pay attention to what is usually done in your country, because there is no shari text to indicate that it is obligatory or mustahabb to do it at a certain time.
Al-Haafiz Ibn Hajar said: The salaf differed concerning the time (for the wedding feast): should it be at the time of the marriage contract, or after it, or just before consummation of the marriage, or after that; it could be at any time from when the marriage contract is first done until after the marriage is consummated. There are several scholarly opinions. End quote.
Fath al-Baari, 9/230
Al-Mawardi, one of the Shaafais, stated that it should be just before consummation of the marriage.
As-Sibki said: What has been narrated concerning the action of the Prophet (blessings and peace of Allah be upon him) is that it comes after consummation of the marriage.
It is as if he was referring to the story of the marriage of Zaynab bint Jahsh, because Anas said: When the day dawned, the Prophet (blessings and peace of Allah be upon him) was a bridegroom to Zaynab, and he invited the people (to a meal).
Al-Bayhaqi included this hadeeth under the heading: Chapter: The time of the waleemah.
End quote from Subul as-Salaam, 1/154
The hadeeth of Anas was narrated by al-Bukhaari (4793) and Muslim (1428) as follows: When the day dawned the Messenger of Allah (blessings and peace of Allah be upon him) was a bridegroom to Zaynab bint Jahsh, whom he married in Madinah, and he invited the people to eat in the forenoon.
According to a version narrated by al-Bukhaari (5166): When the day dawned, the Prophet (blessings and peace of Allah be upon him) was a bridegroom to her, then he invited the people and they had some food.
Shaykh al-Islam Ibn Taymiyah said: The time and description of the waleemah in the hadeeth of Zaynab indicate that it followed consummation of the marriage. End quote.
Al-Ikhtiyaaraat al-Ilmiyyah, p. 346
Al-Haafiz Ibn Hajar said: The hadeeth of Anas clearly indicates that it came after consummation, because he said: When the day dawned, he was a bridegroom to Zaynab and he invited the people â¦
Some of the Maalikis regarded it as mustahabb for it to just before consummation, which should come after it, and this is what people do nowadays. End quote.
Fath al-Baari, 9/231
Al-Mardawi said: It is better to say that the recommended time is flexible; it may be at any time from when the marriage contract is done until the end of the days of the wedding.
That is because there is a report to support that, and because joy is greatest after consummation. But the custom nowadays to do it shortly before consummation. End quote.
Al-Bukhaari said: Chapter on the duty to accept invitations to wedding feasts; the one who gives a waleemah for seven days and the like; the Prophet (blessings and peace of Allah be upon him) did not specify that it should be for one or two days.
Al-Haafiz said: i.e., he did not set a specific time for the waleemah or say that it is obligatory or mustahabb; that may be understood from the general meaning of the hadeeth.
Ad-Dameeri said: The fuqaha' did not set a specific time for the wedding feast, but the correct view is that it should be after consummation of the marriage. The shaykh (i.e., as-Sibki) said: It is permissible to do it before or after; the matter is flexible and it may be done at any time after the marriage contract is done, as was stated by al-Baghawi
Al-Najm al-Wahhaaj, 7/393
Ibn Tuloon said: The more correct view is that one should refer to what is customary.
End quote from Fass al-Khawaatim fima qeela fi'l-Walaa'im, p. 44
Shaykh Saalih al-Fawzaan said: The time for giving the wedding feast flexible, starting from the time of the marriage contract until the end of the days of the wedding.
End quote from al-Mulakhkhas al-Fiqhi, 2/364
There is no set number of guests to be invited; rather that depends on what a person can afford.
Ibn Battaal said: The waleemah (wedding feast) is obligatory, according to one's means. There is no minimum number of people that must be invited.
End quote from Sharh Saheeh al-Bukhaari, 13/283
And he said:
The more you add (to the number of guests) at the wedding feast the better, because that helps to announce the marriage more widely and increases the supplications for blessing of one's family and wealth.
End quote from Sharh Saheeh al-Bukhaari, 13/282.
And Allah knows best.
Reproduced from Islam QA