Hello,
Consider getting Windows Pro if you intend to use more than 16Gb RAM. If not, you won't see any difference between pro and home.
I do not understand well...You have 2 1TB HDD and one is dying and you intend to replace the dead one with a 256GB SSD.You also intend to split the SSD to put OS on c: and samples on the second partition.
That's it?
That seems ok to me,but, if I was you, I'd get 2 SSD's (it seems price is not a problem). One 128GB and one 256GB. A 128GB is something like a hundred euros so it's not that expansive.
I then would put the OS on the 128GB one(should be sufficient) and samples on the 256GB one (if on budget, you may get 2 128GB if 128GB is enough for samples).Why 2 hdds? With 2 separate HDD's you will use 2 sata ports and be able to get full bandwidth for both OS and samples. Imagining the OS is performing an operation while playing, it won't be such an issue if samples are located on another SATA line. Another advantage is that putting the OS on a dedicated SSD will enable to either change the SSD (when it's dead or to small) or reinstall the whole system without bothering backing up you sample libraries. I tend to isolate as much as I can OS from datas.
Concerning drives letters,it won't be a problem for your sessions. Sonar can record audio files in a subdirectory,so if you move the whole directory,you'll always find your audio. It will be a problem for your sample libraries since samplers tend to store full pathes (for halion that's the case). I have set my sample HDD to Z:.That way I can add as many HDDs I want to my computer without bothering about the fact that it can change HDDs orders and name. As long as I set to Z: my sample library, I always get all my samples (and Z: is easy to remember,it's the last one).