1, according to folk parlance, the singular is better (such as 100, 300, 500, 700, 900, etc. Of course, there may be no such taboo in some places.

2. The mantissa plus 1 (e.g. 10 1, 30 1) means reluctant to part, expressing the feelings of mourning for the deceased.

How much money there is depends on the relationship between the two sides and their own economic situation. A few hundred dollars is usually enough.