Quote: "do I need to worry about deleting objects when the player goes out of range or does the engine basically do that for me?"
it depends on the language you're using. Dark basic classic will still draw objects that are outside of the camera range, but the object will be 0x0x0.
Dark Basic Professional will not even try and draw objects beyond the camera range, looks the same, but it has a faster performance.
In either case it's a good idea to delete objects that objects that are too far away from the camera, that way the engine isn't even checking whether or not the object is in range, which increases performance even more. The problem with this is, should an object re-enter the camera range, it will need to be reloaded which may lead to sluggish performance.
Something I read up in the DB classic help pages some years ago was to change such objects into static, it's not something I've ever tried, but the example program for making objects static really boosted the performance. The commands you'll need for this are:
attach object to static
detach object from static
I believe these commands work in DB Pro as well, but I don't have it on this machine... only classic.