Both. Primarily most software written in C should be rewritten to a memory safe language, be it Rust or some other alternative. Because there is a lot of software written in C, this is a veeeeery long term goal, and will probably never be achieved 100%, but at least Microsoft seems to be on board with this.
I don't know, add the sites where the content that you want can be found. I think Jackett also had links to the regular web pages if you want to look around.
I do not use whisparr specifically, but generally for the *arrs you can use jackett to support way more sites. It essentially converts site specific data formats to well known formats that the *arrs support.
Not quite - you get a perpetual license for the version that was released a year before you cancelled your subscription. And for most languages this is not really practical anyway, as they get relatively frequent updates that require IDE updates, so you will just stay subscribed.
This was a fairly low business risk, high PR value move by JetBrains.
No, because this is common terminology that has no reason to be messed with, even if it is technically unclear.