Is custom movement more efficient in terms of processor overhead? Is that what makes it a better choice than Physics? Just curious.
Yes.
One last question (I hope ): Now that I'm no longer using the bullet behavior, what is the best way to set a range for the bullets? My guess would be some version of destroying it over TimeDelta? Also, should I be using TimeDelta to regulate the bullet speed (so it will run the same on different computers)?
Using timedelta in your movement calculations makes the game run at the same relative speed regardless of the frame rate. For example, when the frame rate drops due to lag, objects will perform large steps of movement, which may result in missed collision or other unwanted things. You can also set a special setting for timedelta which remedies the aforementioned problem; it modifies the timedelta if the value gets to low, so that the game goes from "skip frame" lag, to "slowdown lag" if passes a certain threshold. Timedelta is not mandatory however. You can use a fixed frame rate for when you want to program to run with frame based logic, instead of time based logic. Without timedelta however, if you select V-synced framerate, then your game will run at different speeds depending on the monitor's refresh rate. If you need pixel perfect collisions, reliability and consistancy (ie. low res platformer), then use a fixed frame rate. If you want to be able to slowdown time in your game, then you need to incorporate timedelta (there are ways around that but I won't get into that).