need little help about Karma features

[King RoRo]

hello all
I enabled karma feature in my site but i face many problems....
1- how can I set a rule to make member vote once to specific topic or replay ...
2- how can set rule to prevent member to vote to specific member twice ... in other way i need a way to force members vote to another members before they vote 4 a certine one
3- how can i set a permission to prevent members who have less than 20 good point to give a bad vote?


waiting ur assistance please