Before you install, it is worth noting the features that defined this release. Catalina introduced Sidecar, allowing users to use an iPad as a second display, and brought Screen Time to the Mac for the first time.
This generates a compressed DMG file on your Desktop, which is a perfect backup for offline installations.
macOS Catalina run 32-bit applications. If you rely on legacy software (older Adobe CS, Office 2011, many games), do not upgrade. Check your apps using the "System Report" > "Legacy Software" section.