There's your problem. The deployment thread search is using the actual ports schedule info.
Very unlikely any ship will overnight in Le Havre - the world cruise has many one-offs.
The 1/5/24 weekend Freedom sailing is down to $189 for an inside. A few other shorties are decent deals.
https://creative.rccl.com/Sales/Royal/Promotions/rci_sales_event_USD.pdf
The app may still have issues with properly performing the purchase and it's a bit more obvious what you are doing on a bigger screen (assuming you are doing this on a laptop/desktop) in the planner.
Yes, that is generally the way to go. Very rarely (probably by mistake), RCI only puts the single device package on sale where two one device packages are cheaper than a two device package.
Biker, who would purchase via the browser based planner, not the app.
Assuming you are going to a suite where the grats are more than your current cabin, you may not get charged anything extra at all. If anything, you'll get a bill for the diff.
You can use any number of devices concurrently up to the limit of the Voom package - there's no "registration" of a device, the system doesn't distinguish.
The on-board price is likely to be around $26/day