I'm in the process or preparing a lecture on cryptocurrency and have studied dozens of sources. I have a pretty good understanding of most aspects of the bitcoin blockchain scheme. However, all of them have skipped over several points that seem important to me. Here's two:
When does a miner submit his block for verification? Is it when the when the number of transactions reached a certain number, when their total file size reached a certain value or some other criterion?
Does the miner have any flexibility in choosing the transactions to include in his block? Why not just big ones to reach the limit quicker?
Can there be more than one block circulating in the network seeking verification at the same time?