You are thinking like a psychologist or a linguist. I'm not denying that many people view this is a tedious and seemingly silly thing to argue about but you can't metaphorically just throw up you hands and claim that it doesn't matter as a valid counter argument when you are doing philosophy.
The answer to your questions is 'all of the above, to some degree'.
Personally I'd classify "any quantity of discrete articles in which are least one article is held up from contact with the ground/container as being a heap". Heaps are haphazard stacks to me; ergo 2+ items constitute a heap when they are arranged appropriately.
A heap of grain is no longer a heap when spread across furrows (but may be lots of little heaps!).
It's like temperature, a volume of stuff being hot is variable 1K is hot on some circumstances, 10E3 Kelvin if cold in others but we have absolute scales to work around such issues.