How and what do you backup for a simple Oracle DB?
Use RMAN to back up to the network share. An export is NOT a true backup as you cannot perform a point-in-time recovery with it. XE comes with backup scripts that you can just schedule with AT or similar, the documentation says:


  To schedule automatic backups, use any operating system or third party
  task scheduling software to run the supplied backup script for your
  platform


If you are running the database in archivelog mode, then the archived redo logs are your "continuous export", so you would ideally want to have those on seperate disks from the DBFs, and hopefully mirrored. RMAN will back those up too. As you say you have a single disk, well, this is a judgement call you will need to make - I would say if the data is valuable enough to back up, it is valuable enough to run on server-grade hardware.