1) 学完工程专业，再考JD，目标是做专利律师。这条路行得通吗?
It depends. If you do not have a green card, it may be a tough road for you. President Trump is protecting jobs for Americans, not for immigrants. My advice: Get your green card before becoming a JD student.
Listen to the arguments from both sides in the above thread. Make your own decision thereafter.
2) 非理工科读JD能做专利律师吗？
No, you cannot become a patent attorney without a science/technology BS degree unless you have enrolled in enough hard science/technology/college level courses. Check USPTO website for details.
But you can become an IP litigator although you may not be able to work on PTAB cases.
3) 专利律师前景好吗？
It depends. No one can predict the future for you. In a sense, patent law is not that different from corporate law: You only have yourself to blame if you fail.