Howdy, friends - got something for you that's been throwing me.
First, some background, so you know why I'm asking this. In a game of Serpent's Skull my group is running, I'm playing an archaeologist who is slowly creating a personal secretary/database - essentially, an intelligent adamantine tablet that will serve as his own little Jarvis a la Iron Man.
To accomplish this, I have created (with my GM's permission) an intelligent magic item, starting off with a base item that can cast Secret Page at will. The rules for the base item seem fairly clear. Secret Page is a 3rd level sorcerer/wizard spell, so the item must be at least caster level 5, but can be set higher for an increased cost (not that Secret Page does anything different at a higher caster level, but that's neither here nor there). Then you tack on the costs for making an intelligent item, add any desired powers, and voila, item exists, can cast Secret Page at will at caster level 5.
Now for the tricky bits, and thence the questions.
If I later create a similar item (or upgrade the first item, should come out the same no matter how you slice it) to have multiple abilities, either within the base item or as abilities for the intelligent portion of it, then...
How would I rate the caster level?
Still just as the base level required for the highest level spell it can cast, or should it go up as it acquires multiple effects?
If so, does that mean I need to jack up the base price for each of its spells/abilities to meet the higher caster level (again, Secret Page and the like do nothing more beneficial at higher caster levels)?
Say I do jack up the caster level, does that mean that its intelligent item abilities all become more powerful without any corresponding price increase? For example, say the item can cast Fireball 3 times per day at the standard intelligent item ability cost of 18,000 gp - does the damage go up if the base item's caster level increases (not that I intend to do this, but as a hypothetical...)?
[Sidebar question that occurred to me as I was typing this - does the item need to have a base mental stat high enough to cast these spells?]
I feel like I should throw out the caveat here that I'm not trying in any way to create a super powerful magic item to break the game with, or even really to create a particularly useful item - this is almost entirely for flavor purposes. That said, I do want to get it right out of the box, so I'm not just throwing gold away or getting away with making something on the cheap accidentally. Also, I may eventually try to make the item combat relevant in some way, and if that ever becomes the case, then the costs and power levels become much more significant.
Whaddya think, folks?