It depends on your app needs . If you always expect to access all (or most) of the members of the array at the same time then it could an overkill to have separate documents for each member of the array because you would have to do multiple queries to fetch the documents associated with each of the array members.
Now, if the the array size is large, then putting all of it in a single document would have adverse affects as well. Your document will become quite large. We just looked at one case in your question - even if you are only updating a part of the document, you will have to load entire document and write it back to disk which can incur a penalty if doc is large . Document size also has an impact on replication performance.
And yes- if you put everything in one document, likelihood of conflicts increases but if you resolve those, that shouldn’t be a concern.
So couple of questions to consider is whether you expect this array to become very large and if you need access to all members of the array at same time.
Can you raise a separate ticket for this please since its unrelated to the original question .