I would like to suggest that the game proposes 3 orders to chose from when the player gets to receive their next order.
The three proposed orders can be
1) of random difficulty, or
2) easy-medium-long.
New players can then pick the easier orders while advanced players can pick the more difficult orders, if they like. this way, the players will have more freedom to chose which orders they want to fulfil.
If some specific orders are never picked by players, it might be a good idea to modify the required materials.