Hi,
The way to disable autotrim would be to turn off a few flight control computers and put the aircraft in direct law .The message USE MAN PITCH TRIM would appear on PFD and you would use the trim wheel. There is no artificial feel on the stick so it is difficult to fly smoothly (in the sim, never tried it for real) in direct law. This is not an approved procedure, flying in direct law is only ever done as as abnormal procedure.
The lack of thrust lever movement can lead to lack of awareness, if you get behind the plane, it can get a bit confusing. AB say, always know your FMA, this way you should have an idea what the plane is doing. AB also say that you have the option to disconnect and fly like a conventional plane though, as lots of us don't practise this enough, it sometimes causes more problems.
After a few years on the 73, I would say, the bus is generally has less work load and is more comfortable and takes care of pilots errors more. When it goes wrong though, it can get quite complicated, eg the BMI A321 which had a generator problem leading to flickering screens, uncommanded rudder trim, and caused the plane to turn and go 10 miles off course while the poor crew try to work out what is going on. Have fun