some questions - travel to Korea

[mxpweb]

Hey guys!

My uncle will travel to south Korea for the purpose of buying used cars/parts, he never been to there before, as he suggested on me to accompany him, so I would like to ask if anyone traveled to there before:

01). Transportation means available from Seoul airport to Incheon city/province,?

02). What's the best mobile provider - for internet package.

03). Anyone purchased used cars from Korea before? 

04). The biggest markets, used cars yards there? 

Very newbie in this used cars matters, as I need to gather some basic info to be able to assist my uncle in this first trip!

if any additional information about there, will be appreciated, thanks!