The agreement is unconditional
And yet, you then specify conditions. If the vendor gives the breakdown, the purchaser must settle is clearly a conditional term.
Does a material breach of the agreement by the vendor allow the purchaser to withhold payment and/or void the agreement?
You use the term material breach as though you think it has some special legal definition: it doesn't. Unless the term is used (and hopefully defined) in the contract it's not something that would come up in a dispute except perhaps in the argument that the breach was immaterial (i.e. inconsequential). If so, a breach that is not material is not grounds for termination but it doesn't follow that a material breach allows termination.
It's possible that you are using "material breach" when you mean repudiatory breach which does allow termination of the contract.
Each of the following constitutes a repudiatory breach of contract justifying termination at common law:
a breach of condition (as opposed to warranty);
a sufficiently serious breach of an intermediate/innominate term; and
a refusal to perform, known as "renunciation".
Failing to provide the settlement document on time is not a repudiatory breach unless and until the delay becomes so long that it would be reasonable to conclude that the vendor does not intend to supply it - this is more likely to be months rather than days.
With respect to the misrepresentation, I can't see that this is a breach of the contract. Where did the vendor make a representation within (as opposed to before) the contract?
A material misrepresentation (which does have a legal definition) before the contract that induced the purchaser to enter the contract may allow the purchaser to void (not terminate) the contract. However, where the contract explicitly provides a mechanism for adjusting the price, it will be difficult for the purchaser to argue that any misrepresentation a) was material or b) induced them to enter the contract because it is inherent in this mechanism that everyone knows the vendor's figures are merely estimates. It's almost reaching the point where the purchaser would have to prove that the statement was not just misleading but actually fraudulent; that is not just that they were wrong but the vendor knew they were wrong and deliberately concealed the correct figures from the purchaser while they conducted their due dilligence.
If the vendor subsequently supplies a correct adjustment (which reflects turnover less then represented and relied on by the purchaser) is the purchaser obligated to settle, even though the vendor is in breach of the agreement?
A breach where the purchaser does not or can not terminate the contract does not allow them to avoid their obligations - withholding payment would be a breach by the purchaser.
There appears to be no obligation on the purchaser to make payment until the vendor's breakdown has actually been provided. However, as soon as that is done, the purchaser must settle or be in breach.