At last count I have about 30 locos, mostly 1st and 2nd generation diesels, as I model the 1970's. these are everything from Athearn BB's to Atlas to P2K to Genesis, to name a few. All are DC and I don't intend to convert to DCC.
With my small switching layout this is waaay more than I need. But, I would be given to purchasing another loco or two sometime. I like trading out motive power on the layout, so they will all get into service at some time, just not all at once. At any one time I can have from two, up to five locomotives on the layout at once.
I have to say also, with nearly 300 freight cars, this much more than I can have on the layout at one time, but I like trading out as I do with the locomotives.