If you're embarking on a conquest campaign, you MUST build at least a couple of the Constables Palace/Marshall's Palace/Admiralty type buillings for those titles. turning that 5* general into a 7* one is a HUGE boost - it'll take you forever to earn those extra 2 stars the regular way and will almost ensure he's more capable than the commanders he'll be facing.

Likewise those 2 and 3 star commanders. Commanders of this level are pretty common so it's unlikely they'll have an advantage over their oppoennts, but 5+ command generals are much harder to come by. Keeping one of these 2 command granting titles vacant means you can bestow an instant command boost to any general that might need it at home should you facw a counter attack.

Once you get a general up to 6+ stars, he becomes tough to stop and generally starts getting Virtues like Skilled Attacker/Defender etc, because he's always fighting battles and winning.

I can't overstate the importance of a strong commander. The valor boosts they give mean you will take fewer losses and inflict more from the same tropps, and the morale boosts mean your forces will be less likely to break and run, which in turn makes it more likely your opponents forces will.

Going to war with a 4 or 5 star general as your best commander is risky unless it can't be avoided. You want to outrank an enemy general by 2 command or more whenever possible. This sin't to say that you can't win this way, but it'll be harder, take longer and cost you more in both troops and money.

just my 2 cents - good luck!