Chris, I haven't talked with the school representatives or been in the space so you probably have insights that I do not, but I offer the comments below based on my understanding of what you have presented.
Unfortunately, I've had multiple bad experiences resulting from 'two stepping' products and based on those experiences, in making any decision on which products to propose you may want to consider things like whether the product warranties can be transferred or 'passed through' to your Client (if you are not an authorized Dealer then some manufacturers may consider you the Original Purchaser, which is a potential problem for your Client if the warranty is non-transferable), if the manufacturers will provide you direct support (I've had manufacturers limit the support offered to parties other than authorized Dealers), if you need to allow additional time for warranty repairs/replacements due to having to go through the Dealer and so on.
But is that work part of your quote with the E.C. as a subcontractor to you or are you leaving it up to the Owner to handle on their own (and if so, are you planning to define the scope of work required as part of your quote package so they can get it priced)? Have you determined what electrical service is existing and if it may place limitations on what is possible without requiring major changes? If the audio system you are proposing may require thousands or tens of thousands of dollars in associated electrical work then not only may the Owner may want to know that, but you may want to consider it in what you propose.
I understand you may not have exact weights or locations of the arrays but are you comfortable that flying powered arrays is a practical option? It seems to be worth doing some preliminary verification of the viability of flying arrays in general and identifying any limits that might be placed on that approach before proceeding with that concept.
What about speaker grilles being dented in by basketballs and volleyballs? Or if the array is cable or chain supported the potential the dynamic loads that balls hitting an array and possibly even causing it to move might impose?
Is the concept of line arrays with delay fills the result of some preliminary modeling or other coverage prediction or is it more the result of a LAR (Looks About Right) approach? I understand the concept of maximizing the direct-to-reverberant energy ratio in order to improve intelligibility, however perhaps I'm misunderstanding what you propose as with the room dimensions you noted I don't understand using line arrays if they are apparently only going to cover a limited portion of the floor with the delay fills covering the remainder.
Having two arrays is going to double the cost and likely lower the intelligibility for mono sources like speech. Have you considered whether the horizontal pattern of the arrays may be a concern in terms of the resulting energy directed at the side walls or stage? And how does having left and right arrays up front integrate with the side wall delay speakers? Might it actually be less expensive and offer a better result to have one center array along with left and right projectors and screens?
Are you the only company from whom they are soliciting a bid or are they getting multiple, competitive bids? If cost is a factor then I have to believe there are probably less expensive options for what they are trying to achieve than two line arrays plus delay fills.
