1. FastExport should be installed on the edge node. It should never be installed on the database server.
2. It has been shown that a max session count of 4 is generall the best setting, but you can try with more to see if it gets you any better performance.
I do not have an answer for #3.
However, may I ask why you are not using TPT?
TPT supports both an HDFS interface and a TDCH interface for moving data between Teradata and Hadoop.