What is the preferred way to denote orders of magnitude in BTC? If I have 36,235.97 BTC, would I shorten that by writing that I have 36.2k BTC or would I write 36.2 kBTC?

It seems that latter is proper for SI units, while the former is used more often for money, at least in the U.S.
I would write 36.2K BTC.

On the other hand, if I had 0.0362 BTC, I would write 36.2 mBTC.