What precautions to take when flashing Marlin 2.0? I was just informed via a comment that the TH3D Unified firmware a version of Marlin that's no longer updated and considered obsolete (1.9.X in this case) and that, since I'm flashing my firmware to fix my default e-step settings, I might as well flash a non-obsolete firmware.

However, something in the back of my mind is telling me that I can't use Marlin 2.0 because of some hardware limitation.

I'm using the Creality CR-10S printer (with the Creality 2.0 board, I believe) which is an 8-bit CPU. What should I look out for before upgrading to Marlin 2.0?

Marlin's Install website suggests that 8-bit AVR printers can use it (flashing via Arduino IDE). SO I guess I'm double checking before I do something that could potentially brick my printer.
It wasn't advised to use the version 2.x because it was in development for 32-bit micro processors. Now that it has been released as the official version, you can use it for 8-bit micro processors.

But, it totally depends on the amount of options in Marlin you activate (bed leveling, advanced menu, M5xx, etc.). Luckily you can see how large the installation is after you have built it e.g. in PlatformIO. Also, in the configuration files frequently is mentioned how much extra storage activating an option costs (search for PROGMEM in the Marlin sources). Unless you want all options active, you'll be fine. I'm running it on an AVR (MEGA2560) for a CoreXY with bed leveling and some more options; it runs fine.