Best Answer - Chosen by the Asker
The second sentence,"不但没有任何损失，反而获取/得到更多的利益",that would be better.
The forth sentence,"请你帮助我，好让我完成我的作业"，but yours is correct as well
The last one, I thought there's no mistake, while I can understand if there's any connection between the age and dog's paw.
