If you are going to get promoted and don't need a scout to reach your goal (championship, CL qualification, cup win) I would wait for the start of next season (since if you get promoted you get better scouts on the second day of the season).

About the question which one to get? - Go for young scouts that fit into your system.

About which system to play? - That depends on how you want to play (attacking football or compact defense with counters). You can find some infos about systems in the tutorial and the tactics and formation subforums. In the tutorial subforum you find additionally some very well written tutorials.