I think Woelf should probably clarify a bit more on the subject. It seems like he’s saying the choices should be made at the same time unless there is an issue where timing is relevant.
It is an odd gray area. In a competitive environment or with experienced players, the timing will almost always be relevant. At a minimum, player 2 will always want to bring in their +5 selections after player 1 brings in theirs. Ex: If P1 has no events in their starting fleet but brings in one face down via the +5, P2 is more likely to potentially use their +5 to bring in Favor of the Gods or an event/events of their own to stay more competitive. Or if P1 brings in a Black Mark crew face up to turn a ship Cursed, P2 might bring in Soul Mark with their +5.
Considering that it’s usually going to be just crew being added and they generally aren’t getting revealed immediately, all players with a +5 can usually make their choices simultaneously without it really mattering too much. However, if it is an issue somehow, the choice and placement of the extras should follow the same player order established for initial fleet placement.
In a lot of casual games it won’t matter when +5 stuff is brought in, especially since in my experience a lot of people don’t really consider their +5 selections to be modular based on an enemy fleet – they just built a 65 point fleet in the first place for a 60 point game (with 5 points still separate of course). The rules are quite vague on it, so I suppose a play group could play it either way.
I prefer to have it be in turn order rather than at the same time, because the “simultaneous” option could easily get gamey if one player just happens to already have all their crew out and obvious and the other player intentionally delays getting their stuff out and secretly changes some selections based on what they observe.
If a player has both the Hoard ability and “eliminate all of the other ship’s crew” boarding Massacre ability on the same ship and wins a boarding party, can they steal all treasure and eliminate all the enemy crew? (this is distinct from the RtSS Headhunter, who gives an either/or choice)