We should first read the relevant parts of Wang's History of Wei, Jin and Southern Dynasties. Bai Yulin and Zeng Zhihua's Historical Interpretation of the Northern Dynasties and other basic reading materials.
After reading it, you can look at Lv Chunsheng's Studies on the Political History of Northern Qi Dynasty, Yin Xian's Studies on the History of Northern Dynasties, Lei Yiqun's Historical Draft of Northern Zhou Dynasty and other in-depth works.
After that, you can look at the relevant parts of Beiqi Book, Zhou Shu and Zitongzhijian on pages 159 to 177 in Twenty-four History.
After that, you can read Wang's Six Classics of the Northern Zhou Dynasty, Geography of the Northern Zhou Dynasty, Geography of the Northern Qi Dynasty by Shi Yugui, General Classics by Du You, and The First Jizi of Northern Korean Studies.
From shallow to deep, not too much.