Thomas, it is almost impossible to get a handle on Watchtower's finances. You need to BELIEVE what they report to the Government...(who they believe is unworthy of a truthful answer, i.e.: "Theocratic Strategy").
However the buyers of real estate from Watchtower report what they paid for JUST NYC real estate, it was over TWO BILLION DOLLARS. (This site has copies of government files for the purchase/sales on the NYC transactions: https://jwleaks.org/watchtower-properties/ .)
Watchtower attends Wallstreet seminars for high net worth investors, the Morgan Stanley invite made the news, so I suspect a modicum of inhouse or hired expertise. I would expect a modicum of success, so 10% per annum return would be reasonable. NYC sales alone would generate 200 MILLION DOLLARS per year return. That is not including sales in other US CITIES, or STATES, ANY OFFSHORE SALES OR DONATIONS FROM (8 million ?) JWS AROUND THE WORLD. IF 8 million people simply donate $10 per month that would add 80 Million dollars per month to Watchtower's coffers. That is a lot of cash flow even if we cut those numbers in half.