Is it okay to try to sync 120 images for star trails in ACR (level and increase exposure) or will that over-load the program putting all those files in at once?
Opening and processing 120 images with same changes will NOT overload ACR. It is built for that. I routinely open 50 to 200 files in ACR. Then when "Done", what it saves is the small 8 KB XMP files. The large raw files are never modified. Then when you output the 120 final JPG, that might take a few minutes.