Node-RED docker container long startup/deployment time

Of course more nodes will make things slower to load and edit.

You didn't say what kind of deploy you were doing. If you are doing a full deploy then all of your nodes are destroyed and recreated every time, even if you edit just one single thing.

Have a look at this thread. I've linked you to the comment I made about subflows and how there are far more things happening than you might realise.

But you should read the entire thread.