Updating to a new web browser or anti-virus software is not enough to protect your business and may only give you a false sense of security. An unsupported OS will leave you vulnerable to external threats. In fact, a new browser with apps and extensions can introduce new areas for attacks on your system.
Being disconnected to an internal network, or using a USB or CD to transfer information, may reduce the attack surface but will still leave you vulnerable to several types of attacks once support ends. Aside from a few special situations, keeping your Windows XP machine in a sealed room on its own is not the right choice for your business.
Not necessarily. Depending on the age of the device you are using, you may be able to simply update to Windows 8.1 and Office 365. We would recommend at least checking out new hardware though, either because your existing hardware is old (and slow), or because you want the flexibility to work in newer, more mobile ways that new devices enable. You can use the Windows Upgrade Assistant or contact a Microsoft Partner to help make the right decision for your particular situation.
Often, you can. A few old apps may not work on the new Windows. In those cases you can work with the software vendor to get an updated version of the app—which will usually come with additional features and capabilities. In the rare cases where an update is not available, we recommend you work with your Partner or locate a replacement app in the Windows store. Check for app compatibility information in the Windows Compatibility Center.