I have posted about the question of when the island stuff island stuff is filmed too. I think you are right. I think its like a film shot. Where they do it all in one location regardless of when it takes place in the season. I am sure that location is permanently setup so it can be revisted when needed to. So maybe they do a few episodes at a time. This weeks was a perfect example, the flashbacks did not have a direct connection to the main plot. Its also possible that scenes planned for a specific episode are cut for time and are used later.
Its likely one of the reasons Manu Bennett is becoming a regular next season is so there are no restrictions on how often Slade Wilson appears on the island.
I did not think this weeks episode was bad, it was just not as focused as others. Just a lot of hold over plot lines from previous episodes with no real connection.
I like that it appears Helena will not be redeemed. She is a good lesson for Oliver not to go that same route himself. Plus there are lot of potential partners for Oliver being setup. Roy Harper obviously and perhaps Laurel.
I think Detective Lance will be leaving. His character is really one note. He wants to capture "the Hood" and he blames Oliver for his daughter's death. Not much to him than that. Made worse by the fact that the actor seems to have one facial expression!!!!