INT is basically useless. CHA is good for a champion that'll be sitting in a city all the time, but if you want your sovereign to move about, its value drops. And you can drop it all the way down to 5 for no penalty; just a forfeiture of gain. That stuff can go into combat stats and useful traits. Also spell books. Personally, I find the Combat book to be pointless, and Enchantment to be pointless once you get a decent cashflow going (thus making Alchemy superfluous). Terraforming is not necessary, but can be useful at times. Mobility is the only one you should always get no matter what.
Combat magic gives you +5 attack (essentially +10 strength), 50% more dodge, and complete immunity to all special combat effects. This is in addition to shardless direct damage spells, which when coupled with blink, can let your sovereign take on a company of high-attack hammer-weilders without dying. (Fire is a better damage school, but only if you have enough shards.)
Enchantment can grant 25% reduced building construction times and also allows you to insta-build a company of elite hammer wielders (which could take 12 seasons for even the most advanced cities). It also can grant a prestige bonus, which I've found very useful for keeping your city populations growing. (Your cities generate less and less base prestige as the number of cities you own increases. ) Plus, alchemy helps out in the beginning stages.
Honestly, you're best to raise your sovereign as a caster or city figurehead because there are champions out there that have unattainable special abilities. The only thing a sovereign has going for them is the Warrior history, which grants a % bonus to attack, but taking that prevents you from taking Royalty (cities grow 10% faster) or Bard (champion costs are reduced by 25%).
My advice is to bottom out strength and dexterity in your sovereign and hope you can recruit one of the good warrior champions.
