As you have rightly mentioned, the Point in time recovery depends on the Binary logs. The binary log file name and position that correspond to the target point in time you plan the recovery; these are the essential information to be used to carry out the Point in time Recovery.
Binary Logging can be enabled on your CloudSQL Instance by following the steps here[1], and once it is enabled, the Binary Logs are stored for each Automated Backup of your CloudSQL Instance. The Binary logging use storage space on your CloudSQL Instance. However, the Binary logs are deleted with their associated automatic backup every 7 days[2].
You may be concerned about performance on your CloudSQL Instance with the binary logging enabled, well, as per this doc[3], performance of read operations are unaffected by binary logging, regardless of the size of the binary log files.
About estimating how much Data may be lost, I think that depends mainly on your choice of recovery position[4].
I hope this answers your questions.