Unless you're trying to backup system or app data worth more than a hundred bucks, simply rooting your device should be safe enough. I'm sure you know this, but documents, pictures, downloaded files and the like can all be easily copied to a pc without rooting or adding any additional software.
Here's the rooting/rom changing process for the ultra-paranoid:
1. Backup personal data (documents, pictures, screenshots, etc.) to a pc.
2. Root the device
3. Install root backup software and backup important app and system data
4. copy backups to a pc, also.
5. Install CWM or whatever recovery mode your preferred kernel has.
6. boot into recovery mode and create a system backup (and copy that backup to a PC, as always)
7. follow steps for installing whatever rom you want to use.
Disclaimer: I'm a pro with computers, but a relative newbie with smartphones/tablets (and linux in general).