Another hot topic, your points are clear and you capped it in

Part of being an adult is being responsible for oneself and independent

To the questions

1. To ask, yes she can ask but not demanding as demanding money means that the man must 'pay it' while asking means he may deny giving it and the relationship is not affected.

2. There is no defined time to start asking for money but not on the first day you just started. Its more suitable when both parties have had good knowledge of some basic information of each other.

3. The amount should not be fixed in any manner. If for instance she has a need that is likely to consume 1000, she can express to the guy that she has a need likely to take 1k and ask him if he could help her with any amount. Don't expect him to provide all but if he does thank God.

To anonymous 1.
Yes its possible, I dated my fiancee for two years plus without sex. It depends on the individuals involved.
Anonymous 2
My dear it depends on how far the girl went with your brother before they broke up, if they had sex then its a no no for me. If no sex was involved, you can approach her but not without letting your brother know that you are interested to be sure he is not thinking of going back to her.