v5 is pretty faithful to the original in terms of pure 1:1 comparisons; the only things that you would need to take into consideration is bugs with the decomps and which versions you would need to run (1.1.0 should be releasing soon: maybe use that?)
the thing i thought the mods would be most wary of is how easy it is to both create & enable modifications when playing runs, and disable them when watching them back & recording them for a smooth run. For example, you could make a mod that remove Sonic's ability to outrun the camera, making it easier to see what could be coming up ahead. Disabling that before a rewatch would make it virtually indistinguishable from a regular, outrunnable-camera run.
So Sonic Mania got decompiled back in August. I figured you'd already know about this, but I wanted to know if there's any consideration to include times achieved on the decompilation in the leaderboards.