To find some challenge and a new way to play through campaigns, I started fresh on a different server and only played on Brutal. Yes, all campaign achievements from WoL, HoS, LoV and mission packs can be done on Brutal! Searching on YouTube for guide is very helpful, for example, Michael Hsiao has brutal guide for all mastery achievements in HoS and LoV. Indigos Gaming has brutal guide for all 10th anniversary achievement.
Skillwise, I am just Platinum, but I believe game knowledge is far more important than skill in campaign. I did Save and Load a lot.