DPI

I really don't see how DPI could ever affect any of those. The only problem with too low DPI I can think of is pixel-skipping (when minimum mouse read step is too high to move just 1 pixel at low enough sensitivity). The threshold for that depends on your settings (dpi + sens). But it's really easy to test if you have a problem or not: do a minimal mouse movement and see if your reticle moves just 1 pixel or more. If it's more, then you should probably increase dpi (and lower ingame sens to keep it the same).

Too high DPI could result in acceleration, but that's not related to the game in any way, just the imperfection of sensor. I'd say with current sensors, anything up to 3200 or even 6400 dpi is safe (but I can't think of a situation where you would ever need such enormous dpi).