Don't worry about any smooth surface scratching your records, all the information is down in the grooves. If you're caught in a sandstorm, wait 'til it passes and wipe the platter before you place another record, however.
If your tonearm is flat, you can get an idea of the angle by noticing the difference in height between the pivot end, and the stylus end when the stylus is in place on a record. If you stack more stuff under the stylus end without moving the pivot end, you'll be changing the VTA. You might cause that exaggerated sssssssss sound on vocals, called sibilance, among other sonic flaws.
If your tonearm is flat, you can get an idea of the angle by noticing the difference in height between the pivot end, and the stylus end when the stylus is in place on a record. If you stack more stuff under the stylus end without moving the pivot end, you'll be changing the VTA. You might cause that exaggerated sssssssss sound on vocals, called sibilance, among other sonic flaws.