What is the time for the wedding feast (waleemah)?

Firstly: 

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
shar‘i 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 

As-San‘aani said: 

Al-Mawardi, one of the Shaafa‘is, 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 …” 

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-Insaaf, 8/317 

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 

Secondly: 

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.