#1. Kill the fan, (it really is noticeable).
#2. Highpass filter 50Hz 48dB, alone it won’t produce an audible effect, but is necessary if you’re going to subsequently use threshold-dependent effects like compression / de-essing.
#3. De-ess, (e.g. desibilator plugin), that attenuates the brightness only when you are sibilating.
Can de-ess using the high-band of a multi-band compressor plugin on its own.
Gmulti is a good free one which works in Audacity on Windows.
(Currently only 32-bit versions of plugins work in Audacity on Windows, even of your Windows OS is 64-bit).