The vast majority is probably rent/property taxes. With a distant second benchwork (lumber).
Half a mile of 2-rail O-scale track (3-4 mainlines in a 200 foot loop) at today's pricing is under $8 a foot retail. In bulk and pre-pandemic well under $10k total. Considering the budget his roster of engines and rolling stock seems questionable.
Outside of collectable Lionel. Even the high end, magnificent museum quality KOHS brass compounded steam engine will run you ~$8,500. While he is running diesel.
I can understand the appeal of mainline/realistic operations. O-scale has its limitations (normally space) but an NTRAK meet up shows more creativity.
The clip of him using the knock-off Faller Grassmaster is kind of funny.
https://www.youtube.com/watch?v=X-Mcgp6Dtq8