A question with many answers!
It is extremely important to take appropriate precautions, though it's equally important not to become paranoid. Clearly it's necessary to have a professional anti-virus program installed and kept up to date, but one which is effective while not being intrusive.
It is essential also to keep your software up to date as these updates are mainly security related i.e. fixing security holes in the software which could allow a hacker to exploit.
Your wireless network needs to be using the latest security key techniques to prevent a hacker gaining access to your network.
Is your firewall appropriately set so that your network works both efficiently and safely?
These are not necessarily complex or expensive steps to take at all, but can be very costly indeed if not implemented correctly or kept up to date. Software maintenance will ensure all the right steps have been taken to protect your network.