Your equation for FSPL is not in dB. You need either 10 log_10 or 20 log_10 of that value. Whether it's 10 or 20 depends on whether it's in mV or mW.
Also, I think the f term should disappear. I think it's because there is some sort of assumption about the antenna size being related to the wavelength, or something. I guess you've already looked at the Wikipedia page, but if not: https://en.wikipedia.org/wiki/Link_budget
Please let us know if you get anything like useful numbers from this. My experience has been that it really doesn't work in the "real world". I have a simple weather station in my garden which sends data to a receiver in a cupboard the house and I log the RSSI. It's in the same frequency band as bluetooth. It varies dramatically depending on, for example, whether blinds are open or closed in other rooms, whether the ironing board is in that cupboard, where the metal gardening tools are in the garden, and so on.