This sentence confuses me - you want to warm a room, or "any object placed within the enchanted object"?
Or you want something like an oven, that will then warm/enchant some secondary objects, that can then be taken around the covenant as needed?
If you're trying to do it mundanely, like a hot oven that heats stones that are then placed somewhere, and their heat heats the room, then that's possible - but for "light", all you're doing is setting something on fire - there's nothing magical about lighting a torch or six. (And candles tend to melt when heated - not sure if you were going there or not.)
Best might be to make something like a single magical brazier that has a Shape/Material bonus for both heat and light, and enchant it to light/heat an entire room. Both effects are CreoIgnem (tho' different within that), so it should not be hard to hammer out some appropriate Base + Magnitudes effect.
one suggestion for the math:
Base 2: heat to warm
Base 4: light = cloudy day
Item: CrIg 30 effect (Item 39)
(Base 4, +1 Touch, +2 Sun, +2 Room, +1 magnitude for light and heat, +1 Item maintains concentration, +3 levels environmental trigger, +1 level for 2 uses/day)
(Or lose the extra magnitude for light and heat in one, and make 2 items, one Base 2, one Base 4).
If you're trying to make an item that makes a magically heated stone (individual) for a day, that then heats a room - that won't work. Magic does not generally radiate out beyond it's target. You magically heat an individual stone, then 6 of those individuals do not heat the room, just as casting "Heat: Individual" 6 times in the room does not add up to heat the room.
An item that casts a Light effect on objects 6x/day might work, as an "individual" of light is something that does spread out a bit, even if it does not add - 6 magical torchlights do not add up to be the equivalent of light from a cloudy day. ("Torchlight" might be adequate for reading, but for any real work, "cloud day" is probably the minimum any self-respecting magus would want.)
In answer to your question of "how many" torches or candles does it take, the answer is "enough". How big is the room? How high-quality is the torch? How big is the candle? Ars usually doesn't count pennies, so "enough" is the answer - or just a little more than enough. If I were a mage, I'd want at least two - one immediately on my left, and one on my right - for any work that needs to be done. And one more over my shoulder would be nice.