Raising 4, there is a single secondary coil in the ZW. It is probably capable of putting out a continuous 10 amp. The 4 outputs are simply taps on that coil. Doesn't really matter how much you draw from each outlet, as long as the total doesn't exceed 10 amp. How do I get that figure? Rated power is 275 watts. Lionel laste 40's literature said not to exceed 75% continuously. That equates to 200 watts. At the max 20 volt output, this equates to 10 amps. Regardless of the outputted voltage, 10 amps is the most that the secondary coil, OR ANY PORTION OF IT, can take without overheating. This pretty much equates to what GunJohn said.
Do not connect transformers in parallel for a single circuit. When phased, the hots of each are to feed separately insulated blocks. You can have an RW or LW feed a single channel, and that should be adequate for whatever you will practically be running. Before my parents gave me a ZW in late 1940s, I had a single type R, 100 watts rating, running two locos, 2 022 switches, and a #97 coal elevator. I don't recommend emulation.