Online browsing takes very little extra disk space over the operating system.
For file sharing, assuming this is the file server, then you have to do the sums as to how much space you will need. Allow 75 GB for the operating system and its updates, anti-virus programs, browsers, etc. and the rest for you shared files.
If this is the client machine, then you possibly need only a few GB to hold intermediate files.
I hope this helps.
Offline storage doesn't really have anything to do with online browsing.
As far as file sharing, that would of course depend on the number of files you plan on dealing with.
That is way more than enough space. I do wonder what you mean by "file sharing" because that could take a lot of space depending on how large the files you are sharing.
It depends on what files you share, but it's usually enough.
Yes, that is plenty.
The things that use up a lot of space are videos or recordings of game play.
Even so 750 Gb gives you plenty of space.
Yes, that's more than enough