...I cannot afford to brick the tablet.
Jeff
You probably don't want to approach a project like rooting and installing a custom ROM when it involves a tablet you're not willing to brick, especially if this is your first attempt. Don't take this warning lightly.
But if you really want to do this, bookmark this page in case things go wrong and you need to re-flash a valid stock ROM to restore your Tab to working condition:
Stock ROM download:
https://updato.com/firmware-archive-select-model?q=sm-t520&exact=1
Instructions:
https://updato.com/how-to/how-to-install-an-official-samsung-stock-firmware-using-odin
If something does go wrong, hopefully it'll just be a soft-brick you can readily correct. If a hard-brick that's a worst-case scenario.
The first thing to do is make sure you have a backup of your data. Install Samsung's 'Smart Switch' utility on a computer and do a full backup.
https://www.samsung.com/us/smart-switch/
If you're using Windows this also installs the latest Samsung driver, a significant point as the connectivity between your Tab and your computer is a significant point.
You'll also need to install the Odin utility on your Windows PC to do the actual flashing. Most online directions refer to using the latest version (currently 3.13.x) but note that Odin often has backwards compatibility issues so you might find it to be a lot less hassle to just install an earlier version that's appropriate for the hardware/firmware you're working with. See below:
https://www.droidviews.com/download-odin-tool-for-samsung-galaxy-devices-all-versions/
Also, Odin is a Windows utility so if you don't have access to a Windows PC there's also 'Heimdall', and Open Source alternative to Odin. It's available for Linux, Mac, and Windows:
https://www.glassechidna.com.au/heimdall/
It's not an exact equivalent so you have to be more flexible as a lot of the menus are in different arrangements and things like that but it's functionally the same.
As for the rooting process, try using this guide:
https://androidmtk.com/root-samsung-galaxy-tab-pro-10-1-sm-t520
Once rooted, you'll want to install a custom Recovery like TWRP:
https://twrp.me/app/
https://play.google.com/store/apps/details?id=me.twrp.twrpapp
At this point I'd use your Tab for a day or two to make sure everything is OK and working properly before flashing a custom ROM on it.
https://www.makeuseof.com/tag/what-is-a-nandroid-backup-and-how-exactly-does-it-work/
