This is a bit off-topic. One of the prerequisites to create a strong empire for the Murongs is to lay a strong foundation, and by that means:
1. Have enough money reserves. I'm certain that if Murong Fu sold his manor and his cupboard of martial arts manuals, he would have plenty of cash to spend...
2. Start recruiting and train up a strong army (Clearly the Murong Family didn't have this...)
3. Hire mercenaries (like Zhao Min did) to serve the Murong Family, even if they only have bit part abilties, numbers would make up the quality somehow. (People like Bao Butong aren't that good, but having 20 Bao Butong would be a different proposition)
4. Improve your martial arts. (Murong Fu didn't trained hard, it's a waste given that he has some talent in martial arts and that cupboard of martial arts manuals - imagine a Yan Emperor that is strong in martial arts, people would be scared of that.)
5. Have more interest in women, take in more concubines. Imagine if MRF take Wang Yuyan as his wife, Ah Zhu and Ah Bi as his concubines. With such great women by his side, he can use their beauty and intelligence to plan some devious acts. (Clearly, he didn't appreciate them, especially WYY)
5. Wait for the right moment to strike (MRB and MRF waited for this, but they didn't have Lady Luck around to pull off their plans)