Please go through the below link from Mendix documentation and if you still have any questions we can discuss more on tjem.
2- Yes we can. See logs on developer portal > App > Logs
1- Shortly, most of the time other then debug and trace log levels are enough to follow and find out what is going out- working and/or not working- , but in case you need more insight and more details, then trace is good to go with. You can expect so much flow and details.
Track Application Behavior with Logging on Mendix academy.