I went for the position last year, and reccommend your idea of going on as many visits as possible.
I managed to learn the taxiways and most of the stands from the a/d layout, but its completely different when in the tower. I never passed the assessment, but this was because i never went on a visit, and i was told this on the feedback.
The assessment is quite relaxed, and provided you put in the work you should get on fine.
Best of luck