As'alaamu Alaikkum,
The answers below to your question are my opinions only and may Allah Subhana Wa T'ala forgive me if they are misleading away from the truth.
1. Why Islam didn't abolish the tradition of Slavery?
Slavery has always been with mankind, whether we like it or not some people are blessed more than others and not everybody is equal. It is like a bounty given to you. Equality is a recent concept when people looked away from the laws of God and followed the laws of shaytaan.
Muhsin Khan
He sets forth for you a parable from your ownselves, - Do you have partners among those whom your right hands possess (i.e your slaves) to share as equals in the wealth We have bestowed on you? Whom you fear as you fear each other? Thus do We explain the signs in detail to a people who have sense.
Nay, but those who do wrong follow their own lusts without knowledge, Then who will guide him whom Allah has sent astray? And for such there will be no helpers.
30:28-29
2. When a slave girl is taken as maal-e-ghanimat, how can a man be allowed to have intercourse with her without her permission? is Islam so biased towards females??
Please provide proof where these situations have occurred.
3. Why can a man beat his wife if she is ignorant but a wife can't if her husband is ignorant?
Only ignorant men beat their wives, no matter what the religion is.
4. Why is Islam against family planning?
In Islam it is a blessing for a man and wife to have a loving relationship and to have children. Family planning is a recent invention invented to reduce the 'unwanted' pregnancies that happen between unwed young people, as a result of fornication and family planning in fact encourages it.
5. Why will more women go in hell than men? And why menstruation is considered a cause of deficiency of 'imaan' in women even thought its not the fault of a women to get menses.
Narrated Abu Sa`id Al-Khudri:
Once Allah's Apostle went out to the Musalla (to offer the prayer) o `Id-al-Adha or Al-Fitr prayer. Then he passed by the women and said, "O women! Give alms, as I have seen that the majority of the dwellers of Hell-fire were you (women)." They asked, "Why is it so, O Allah's Apostle ?" He replied, "You curse frequently and are ungrateful to your husbands. I have not seen anyone more deficient in intelligence and religion than you. A cautious sensible man could be led astray by some of you." The women asked, "O Allah's Apostle! What is deficient in our intelligence and religion?" He said, "Is not the evidence of two women equal to the witness of one man?" They replied in the affirmative. He said, "This is the deficiency in her intelligence. Isn't it true that a woman can neither pray nor fast during her menses?" The women replied in the affirmative. He said, "This is the deficiency in her religion."
Book 6, Hadith 9English reference: Vol. 1, Book 6, Hadith 301
Arabic reference : Book 6, Hadith 305
Having menses does not make a woman deficient in imaan, rather the reason they are not allowed to pray is because menses are deemed as unclean by Allah Subhana Wa Ta'ala. In fact any bodily discharge is unclean. One has to be pure in body and in spirit to appear before Allah Subhana Wa Ta'ala.