That's a puzzle to me. You're setting yourself up for extra clicks and manual operations, and for what benefit?

You can set Thunderbird not to automatically download new messages at start up, and also disable the automatic download at regular intervals. I'm not sure this will be 100% effective if you use IMAP. You should also try changing the "Idle" setting.

To defer sending, you either use a Send Later option which parks outgoing messages in the Outbox (more clicks) or you toggle Thunderbird between offline and online (again, more clicks).

You have more work to do and the risk of forgetting to collect or send messages. That's one of the reasons we use computers; to attend to repetitive and mundane chores.

What you are used to and prefer made sense 20 years ago when the Internet was purely dial-up. You would concentrate all your uploading and downloading into a single short session and then drop the connection.

I don't spend all day in front of a computer so one extra click to send mail, or one click to pull mail doesn't materially effect me. The advantage of what I'm looking for is that I can write a message, or a reply, and leave it in the OUT box in case I want to modify my message, usually after reading more from my in box. The advantage to requesting mail from the server, rather than automatically receiving it, is that I can process all the older mail before attacking the new mail. So... I unchecked the "Check for new messages on startup" and "check messages ever __ minutes" boxes, but I still get messages rather than the program waiting for me to press "Get messages." I do have an imap server.

Set the account up using POP. POP is a "fetch" protocol, so when those automatic download options are disabled, it will only get when you tell it to.

The advice about sending stands; work offline or use Send Later.