I've always assumed that one can only get one Shape and one Material bonus. Usually it turns out to be just one unless its a Compound item. But I was rereading the MRB and it indicates that you add up "all" of the bonuses available.
So can you get multiple bonuses on enchantments? Two or more of Shape/Form even?
Don't forget your S&M bonus is capped by magic theory. So there's a limit to how much stacking is worthwhile. Chances are one shape bonus and one material bonus will get you to your cap, so adding any more ceases to have any effect.
Also remember that the lab text that results must incorporate all shape+material bonuses used, so any replication must use the same bonuses. This can potentially reduce its trade value - a heavily stacked item made by someone with a magic theory of 10 results in a lab text that may require the addition of lots of expensive extra bits that grant the second magus absolutely no benefit (aside from the benefit of working from a lab text, obviously).
It doesn't matter that much because it is capped by MT.
I'm not sure it comes up all that often, but the passage I think you're referring to says, "It is also possible to prepare a compound item for enchantment, so that you get the shape and material bonuses from all the components for all effects." Not all effects might be able to take advantage of all the bonuses available, and then it is going to limited by the MT score.
So the answer is "as many bonuses as you can fit into your MT." 
If I want to design an item that will turn a person into a wolf, I'd certainly be using a wofskin cloak.
That's +7 for wolf skin and +4 for the cloak part.
Too bad my MT is only 4, so any old cloak would been just as fine. (Because as everyone has mentioned, the bonus is capped by MT).
But if you were to make the cloak out of wolfskin, using both the +7 for the wolf skin and the +4 for being a cloak - even if you yourself only get "credit" for +4 S/M Bonus because your MT is 4, could not another magus with a MT of 11 then come along and, using the same lab text, use the Wolf Skin and the Cloak and thus get credit for +11 to his Lab Total?
So I believe.
Ofcourse, he'd hardly need any Arts by then 
The way I do it is that a shape and material bonus must be intentionally included in the lab text.
The lab text for the cloak that includes the +4 shape/material bonus for the cloak could be applied to any cloak (not just wolfskin ones), and the subsequent magus with MT 11 would not be able to leverage the +7 bonus because it is not part of the lab text. The original author could theoretically choose to include both cloak and wolfskin as S&M bonuses (despite not being able to leverage both) - in this situation the lab text would require a cloak that is wolfskin, and the second magus could leverage both bonuses. This scenario would be extremely rare, as the first magus has no reason to include the wolfskin bonus and good reason not to (it limits the flexibility of the text).
This also allows for generic lab texts - a text that makes use of no shape or material bonus can be enchanted into anything, but the magus may not use any S&M bonus of the target item because the lab text does not include them.
It also makes item text trading more interesting. Unwanted S&M bonuses for lab texts from other magi means either having to reinvent the text or somehow integrate the bonus into the item. The easiest way would be to incorporate a symbolic representation of the shape bonus into the target item, or incorporate some additional materials. Sure, it means your enchanted robe ends up covered in symbols... but robes covered in strange symbols isn't exactly against type for a magus. 
This is how I handle it. YSMV, of course.
Answer= "as many bonuses from as many S/M categories that fit under your MT."... True or False?
True.
The classic example is a wand that is enchanted to project some sort of "death arrow".
In this case both the bonuses "+3 project bolt or other missile" and "+4 destroy things at a distance" could be utilized.
Assuming people are things, if that's what you meant.
Yes.
Actually I've always thought of this as the "+3 project bolt or missile" for effects creating a medium which damages (like CrIg - Pilum of Fire) while the "+4 destroy things at a distance" for direct damage/destruction effects (like...PeTe - Pit of the Gaping Earth). Two different things.
I would surely argue against those wanting to apply both.
Sure, some particular effects would only get one bonus or the other, but it is hard to see why an effect like a "death arrow" would not be both "a missle" and an attempt "to destroy something at a distance".
It's not a big bonus, and the total is still limited by your MT.
YSMV.
Destroy as in Perdo perhaps rather than Creo something that inflicts damage. I think it is a fair distinction and of course YSMV.
Now that you remind me, I would argue the same but because they both come from the same Shape.
That is the whole point of the example!
The RAW tells us to inspect the Shape and Material bonuses for the shape and material and if any bonus matches the effect, to add that bonus to the Lab Total. The total Shape and Material bonus cannot exceed your Magic Theory, but the RAW does not tell us that you only get one bonus per shape (AFAIK).
Usually, you do only get one bonus from the shape, but that is because most shapes only have a single bonus. But if several apply to the effect in question, you apply them all.
Another example, would be a Cloak that "transforms the wearer" to give him wings that enable him to "fly"; the bonuses +3 flight and +4 transform wearer are both applied.
Just to clarify,
The total benefit from form and material bonuses cannot exceed your MT? ie +4, +7 = 11 MT 10 only gets a +10
(as opposed to the individual bonuses cannot exceed your MT?) ie +4, +7 = +11, MT 6 only gets a +10
Surely that makes the heavily compounded talismans and Items of Quality far less effective?
I've always assumed that only house Verdi could use the symbolic representation of a form is that incorrect?, eg carving a symbolic wand into the stock of a crossbow to give it the "+3 project bolt or other missile" bonus. (one that makes perfect sense, as there is no crossbow in the F&M list (AFAIR).
Although one item I've been debating was mentally nicknamed "The big A-Z of Verdi symbols" containing representative symbols and materials of everything I could fit in one book... (about 15 items at last count), would make an interesting talisman.
K.
As I understand, yes.
Yes and no. Such an item can provide a bunos for a large number of different uses and situations.
I could make a talisman that would help me with creating fire and transforming myself into a beast.
The bonus to producing fire could be no larger than my MT score, but if I sometimes want to transform into a wolf, I could get bonus up to my MT to that as well.
HoH: MC p. 124 is fairly explicit about only ever letting an item get a single bonus - I've always read this as a single bonus from a single source. Ever.
Making the issue of compunded items moot.
I must admire your mastery of Magic theory to make this item though!
As per ArM5, p97 a compound item can have no more components than your MT score, meaning you'd need an MT score of 15+ to invest that talisman, having spent no less than 600 XPs on the project (400 with an Affinity).