Here i will suggest some options i use to amuse the solo play Vs the GT AI with random maps and oobs for the game patched with 01b (for further patches will improve the game itself).
GT AI should not have less than 5 Corps (as reported in the manual)
GT AI should have one Corp more than yours, for the GT AI will always leave one Corp for LOP defence.
Giving one Corp more the GT AI will have the same "mass of engagement" that the player puts on the field to match your Army.
I suggest that GT AI CEH should be 10 points (average) bigger than Player's CEH.
Corps for the GT AI should have an average of 6 (or more) infantry units, 3 (or more) cavalry units, and, regarding artillery (as reported by another user) the unit should have from 5 to 7 artillery units (except regimental guns); with such a Corp i saw the GT AI press me really well on the field of battle.
If you do not want to buy every single unit for the GT AI i suggest to make a random Oob and make just some little editing.
I often play with 100 CEH average on 15 Km maps and, being unable to cover all the field of battle i can say solo battles are really amusing.
Those above are just suggestions, hope this can help