Interesting screenshots of internal WT databases appear in the 2018 Coordinators' Committee Report video (that's in fact a presentation of their HuB software) at 6:34-6:50. They contain, among others, the following information:
there are 61,349 Kingdom Halls and 841 Assembly Halls;
4,308 properties are held for sale, including 2,925 KHs;
1,473 properties have been sold in 2017 and 2018 service years;
784 KH property purchases and 1,130 new KH projects are in progress.
Two things need to be mentioned:
I found this info here;
of course, it should be taken with a grain of salt.