There's a pricing example on Delta Vacations that might shed some light on how it works. Booking through Delta Vacations requires a car and/or hotel add-on; presumably other sales channels would not have this requirement.

My guess is that when purchasing the pass you would need to specify how many coupons and in which zones in order to calculate the price, but could actually make the reservations for the flights (after the first) later. You would just need to have a coupon for the zone corresponding to the flight you want to take. Might want to find out who to contact to make those reservations, since perhaps not all agents (DL agents, anyway) would know how to do this.

Note the fine print: "Prices do not include taxes." That's reasonable, since taxes vary by routing, e.g. UK departures. However, it would be important to confirm whether prices do include YQ; if not, that could be significant additional cost.

Also note "earn miles on all your flights (some restrictions may apply)." The restriction likely would be whether the fare class on that particular carrier earns full, partial, or no miles on the program you're crediting miles to. It would be necessary to find out what fare class these book into, in order to anticipate how many miles (and MQMs and medallion bonus miles) will be earned.