How should I get started with LEGO trains?
That set would work, set 60052 would work as well (although it has a few more parts that are not actually needed if you are really focused on trains, in that regard 60098 might be better)

Those sets (including 60051) are from 2014/2015, rumours have it that new trains will come out this year (probably around august), and apparently (I hadn't heard it before @TheBrickBlogger wrote it in a comment here) they won't be completely compatible.