It's been a while since I built mine, but I'm pretty sure it supports 4 serial interfaces. At any rate, Oscar had a VT220 hooked up to a PiDP-11 at VCF ZH 2019.
Yes it supports up to 4 serial interfaces given the ports available on the Pi. You can use small USB-to-RS232 converters, and/or use the built-in USB-to-serial plus additional USB-to-serial converters and solder two MAX232 chips on the board.
I have mine connected to a TeleVideo terminal.
I'm pretty sure you could do a lot better than 4 ports...
Sure, but to what end? You've got 4 RS-232 devices, plus the Pi's onboard TTL serial console, and the VDU console as well. A TU-58, a papertape reader and punch, a plotter...?