We used to use artillery corps quite often in our campaign games. 3 or 4 batteries to the corps. We then fielded limited artillery pieces (ie 1 gun per 1 ceh, so a 200 ceh army would have 200 guns of which only 25% could be 12pdrs) with 6,8 or 10 guns to a battery. Very good for defensive strategies, but because of the frontage of these 'grand batteries' it becomes very awkward when using them offensively.
The above 'rule' was used to stop sillyness with huge artillery armies and all artillery being 12 pdrs in mp games, we found the game ai handled smaller batteries better... 10 or 12 guns per battery max.
With new game engine changes I cannot say how they would perform now as I haven't used a formation of this type for a long while.
But, if I was to field one now I would definitely support it with a small cavalry corps using the link order, to have infantry within the corps itself may mean that not all guns would be used on the frontline, therefore nullifying the formation as a grand battery...
We never used a reserve, all guns would be placed on the frontline maximising the power of the all artillery corps. Definitely mix the gun calibre types ie 6, 8 and 12pdrs and howizters, try to keep only 2 calibres per battery, ie 6x6 pdr + 2 howis. 6x8 pdr + 2 howis. 8x1 pdr + 2howis and so on... hope this helps.