Being connected to the internet is generally not the issue. It is what the OS, programs or you are doing on it that counts.
Basically disable/turn off automatic checking for updates for the OS or programs. Instead, choose a non-critical time to manually check for updates and do the associated downloads and installation.
Only surf to the official sites for your programs. Definitely don’t have any email checking programs, as they tend to do their internet stuff in bursts, and often enough that they are likely to disrupt a recording/mixing session.
As for anti-virus, I use Windows Defender, which on Win8.x includes AV. On Win 7, I used MS security Essentials, which is basically what is now in Defender. They generally have low system impact.
There are two levels of backups:
a) System, which does images of the OS and system drives.
The latter, though the system backup could be used for that, is more flexible for retrieval if it is done file for file, rather than by whole disk/partitiion image.
Note that not all file-by-file programs actually copy all files. Some free ones like mirror and SyncToy seems to forget to copy some files, and they don’t let you know. I use SyncBack Free, which I have verified does all files. Note that generally file-by-file programs don’t handle super long filenames or paths (the OS cannot copy them), nor files in use, so only run them off-peak.
As for system backups, while the OS’s system backup utility can do automatic backups, retrieving them reliably is not a given, and especially bad if you somehow need to restore to a partition that is smaller than the image made.
Win 8.x has basically deprecated the system backup, and I found it more finicky about what it will restore to. I now use AOMEI Backupper, which is free, but importantly allows resizing of backup file to fit smaller restoration targets. Their free partition manager has also been a life saver, especially when I needed to fix up a troublesome restore from a Win system backup.