There’s no hard limit on how many potential actions a ship could generate in a single turn. It just can’t do more than two.
In your example, as long as you haven’t already started any part of the repeated move action from the SAT, you can use the SAC to take a completely different action instead.
You have to place the first one that gets found on the island. Any more than that (up to 10 total) is entirely up to the player who found it. Granted, I can’t think of any good reasons not to place them all, aside from being short on physical markers or tokens to actually represent them. (I’m still a little disappointed that whoever did the art/layout missed filling the entire card with turtles, as originally intended.)
Is Odin’s Revenge reusable with Nemo’s Plans? I assume it would be a once per round option on that player’s turn?
It can be reused once per turn.
I can’t find anything for it. You’ll have to work that one backward from other known values.
The files I have say Uncommon, and that’s also consistent with the ship type.
It’s most likely a misprint of the rarity, which isn’t surprising because that happened numerous times across the various sets. It’s good info to include in the master spreadsheet, but it’s not something the PC needs to address beyond the notes about it already on the first and last pages.