If you have a custom recovery already, where Clockwork Mod Recovery is the most popular one, there's an option there to do a complete backup, sometimes called a "nandroid". As long as you have this backup folder lying around (it won't disappear when doing wipes from CWM) and you can enter CWM, you can restore that backup as well. Since the backup includes everything it also includes things like the kernel, the ROM, apps and all that. It basically creates an image of your entire device that you can later return to.
The tricky part is getting a custom recovery on your tab, but when you have that you should be reasonably safe as long as you remember to always backup. It doesn't hurt to put your backups somewhere else as well for safekeeping (like your computer).
I highly recommend you start reading the Samsung Galaxy Tab forums on xda-developers. The Q&A section probably already has all your questions listed, and the "Android Development" section has a ton of different ROMs you can choose from. As long as you have a backup lying around, don't be scared to try a couple of them out :)
(Remember that rooting your device and/or unlocking the bootloader will void the warranty, so if you can't re-lock it before sending it to Samsung they will not replace it)