I currently have about 350 .com domains. At one point I had almost 1,400. When I had >1,000 I would sell 1.5-1.8% of my domains per year (almost 2 per month).
However, the carrying (renewal) costs were too high, so I lowered down. 95% brandables, a few geos/keywords. Now with ~350 I sell ~2.7% per year (about 1 per month). But of course carrying costs are lower.
Most are hand regged, but a small % are drops/expires. Average sale price since inception is just over $600.
Over the 6 years I've been doing this I basically broke even (although I still have about $20k in sunk costs with my remaining 350 names which I'll need to recoup to continue to break even). I suppose with more quality I could start to see some profit - but with such a small portfolio and avg sales price - it's not going to be much profit. Will whittle down portfolio to ~300 names in 2019.
Sales come from the following places:
58% GoDaddy Premium
15% Direct
10% Sedo
8% GoDaddy Auctions
8% Afternic* (only live the past 18 mos)
2% Brandbucket