As @ChrisGorgolewski says, it’s difficult to predict. We try to estimate within the program, to reduce the chance of hitting memory limits unnecessarily.
While I can’t tell you how much memory you will use, I can attempt to address your situation. The most common cause I’ve seen for running out of memory is a large BOLD series (>700 or so TRs). If this is your situation and you aren’t constrained for disk space in your working directory, consider using the --low-mem flag (even though it seems you can request plenty of memory). This will wait until the end of the pipeline to compress the resampled BOLD series, which allows tasks that need to read these files to read only the necessary parts of the file into memory.