Creality CR-10 board upgrade from V1.0 to V2.0 questions
Any issues compatibility wise or firmware wise that I might run into while upgrading

These boards are 8-bit boards with limited storage capacity for your firmware, if you would need an update, as an alternative solution, a 32-bit board may be a much better solution.

Also I know that the V2.5 board uses Marlin firmware, is that the same firmware that the V1.0 uses

I do not own this board so I can't say for sure, a generic remark would be that the Marlin 2.x branch works fine on 8-bit boards (from experience with some of my own boards), but you frequently see (does not have be the case for this board!) that these OEMs use the latest from the 1.1.9 branch. The only drawback is that you sometimes need to be creative to fit the firmware on the board, the more options, the more memory is used.

Is it worth it to upgrade to BLTouch

That depends on the state of your heated bed/build platform. If the build platform is not flat, but is somewhat curved, you may see improvements in bed adhesion when you correctly add a sensor that maps the surface and adjusts for it during printing. If it is flat, manual leveling works fine.

I am not that clear on whether you would have to ever use the manual bed leveling adjustments or does BLTouch take care of that forever?

Even when using a sensor that maps the surface of the build platform, you should always try to deliver a bed that is as level as possible. In videos you often see the bed tilted (very much exaggerated); you need to remember that the printer will print in a plain level after about 10 mm (or to a different height, determined in your firmware or set by G-code), a skew platform will give you a skew print.