Sorry to say, but I think that listing is almost bound to be problematic. Technically, it's a type of choice listing, some of which are allowed and some of which are not, and I suspect yours is not (choice listings that are Ok are items where there is a minor variation on the same item, such as colour, and/or there is a customisation option, as long as there are no further costs etc).
An example of a choice listing that isn't allowed is something like a listing for 50 individual CDs, where the buyer purchases a quantity and selects the titles they want from a list, and I think your listing would fall into that category.
That aside, and on to the actual issue... The listing is pretty clear (to me) about what is being offered and how etc, but there are numerous members who will not read the details in full. That is their problem, to be sure, but all too often it becomes the seller's problem, and the potential for confusion is quite great for a listing like that, and I wouldn't be surprised if someone came along (possibly your buyer) and thought $25 would buy the whole lot shown in the gallery pic. If you don't hear back from them soon, I would send a message with whatever information I felt suitable, and let them know that in order to prevent delays to postage, selections would be made randomly if choices can not be confirmed by X date and time (I would give at least 24 hours, all things considered).
I feel you would be better off listing in a different way, as other problems may arise, eg more than one buyer purchasing around the same time, with one or more of the same item in their lists.
