There is no limit set by Islamic Law for either the maximum or minimum amount that the dowry can be.
Allah says: “Even if you had given one of them a mountain of gold as dowry, take not the least bit of it back.” [Sûrah al-Nisâ: 20]
He says: “Give them their dowries as prescribed” [Sûrah al-Nisâ: 24]
He says: “And give women their dowries as a free gift.” [Sûrah al-Nisâ’: 4]
The Prophet (peace be upon him) said to the man who wished to marry the woman who had offered herself to the Prophet (peace be upon him) for marriage: “Produce something, if but a ring of iron.” Ultimately, the Prophet (peace be upon him) married her to him for what he possessed of the Qur’ân. [Sahîh al-Bukhârî (5135) and Sahîh Muslim (1425)]
Some schools of thought have imposed upon the dowry a minimum limit of ten dirhams. However, this opinion is not supported up by any textual evidence.
The dowries that men must pay is something determined by custom. Such customs are upheld as long as they do not violate the dictates of the sacred texts or the general principles of Islamic Law and as long as they do not result in general harm. For instance, if the customs of a society set the dowries so high that people abandon or delay marriage on account of their inability to pay, then measures can be taken to remedy the situation.
Islamic Law encourages the facilitation of marriage so that it is an easy matter. It discourages excessively high dowries.
The Prophet (peace be upon him) said: “The women possessing the greatest blessings are those who require the least demanding of dowries.” [Musnad Ahmad (44595)]
The Prophet (peace be upon him) never gave any of his wives – and likewise never demanding for his daughters – more than 10 ounces of silver. [Sunan al-Tirmidhî (1114), Sunan al-Nasâ’î (3349), Sunan Abî Dâwûd (2106), and Sunan Ibn Mâjah (1887)]
The dowry can be deferred in its entirety to a later time, or deferred partially, without any problem.
And Allah knows best.