My opinion, sell him if he isn't playing well. He will be a 5 star next season. Buy another 5-star DC-DMC at auction and then sell the one you have.

If you buy scouts, do it at the start of the season. From what I've gathered on here, 3rd season is an easy season with a lot of neglected teams. I'm level 2, and only 4 teams are active in my league. I plan on holding out till level 4 before I consider buying scouts.