1-a kafir is someone who does not believe in islam. although islam was the religion of moses and jesus,it was completed with muhammed and therefore if this completion is not believed the person is a kafir. this is because kufr means disbelief and therefore the people of christ and moses disbelived in the final message.
2- of course a jew can become a muslim, if he believes in allah and his final messenger.
3- i will try to come back to this question as i cannot find the literature on it at present.
4- islam, believe it or not, came and gave women so much fundamental human rights that they never enjoyed before. it is the misconception that since she wears a headscarf and loose clothing that she is nothing. this is not so. you will see those models who are on the catwalk as being more liberated than them but this is not so. those models are sold as would cattle in a meat market, and the price for them to be BOUGHT will be according to their height, weight, hair colour, eye colour etc. now this is a women who is treated as a second class human being!
as for the muslim woman, she has exactly the same rights as men. if anything she is meant to be treated very well by her husband and he has to provide for her physically, emotionally and financially. she has a right to work, as the prophets first wife was a business women. it is only recommended that she does not work when she has kids as they are going to represent the future generation and therefore she cannot neglect their careful upbringing. men and women have been given specified roles, this is not discrimination but it makes their lives compatable. as we see men and women are genetically, emotionally and physically different, and therfore have been given their roles accordingly.
6- the rewards in paradise are as they are due to the things we had to give up in this world. nothing is sinful, i dont think, and the numbers of husbands and wives are the same amount for each, although i dont think the figure you gave was correct. the person will be in his youth and will stay like that forever.
7- what awaits a muslim woman in heaven is exactly the same as that awaits man, except women will be married to men! when islam came the quran stated that believing men AND women have duties and have rewards, and therefore it does not discriminate as people tend to think.
9- a division between darul islam and dar ul kufr, i think it is supposed to be. this means that for muslims a lifestyle of islam should be provided and this can only be accomplished in dar ul islam, as for dar ul kufr, this is muslims living under a system which does not implement any islamic values, therefore this can prove very hazardous for muslims in the long run, as they will lose value for the way they are supposed to practice their religion.
10- the prophet,peace be upon him, received the revelation of islam and as he did he practiced what it taught, as his wife aisha said he was the living example of the quraan. the quraan also states that the prophet only said and done things by his will and therefore god told us that whatever the prophet said we had to follow as he had authority. therefore as the muslims have to live according to the quraan who better to follow than the prophet as he was the best at this. also all the teachings he taught which are hadith are for our benefit and we have to follow that too.
as for the beard, there are many schools of thought which interpret the hadith about the beard. men do have to keep beards, and the length depends on which school you follow.
for those who do not keep beards, they are no less muslims than any other, it is only that they are not practicing this teaching.
11- god is all knowing all wise and whatever he did he did for a reason, and maybe because the revelations did end during his death that god decided to take him. there is nothing that i know on this in the quraan or hadith and therefore i can not exercise my thoughts as i have no knowledge on this.