is it possible, we can have tracing/profiler ON for a single user in place of the whole store. This can make sure that the load is not heavy even if we start profiler during peak hours.
Yes. You can add a filter in the profiler on the "Filters Tab". You could then specify to log output for just that user. The system management guide has details on configuring this. However, I do not think this will impact the system load, though. Everything might still be processed and it is just being post-processed to only log relevant events.