I am working on a small project for work. I am trying to figure out if you can connect 3-4 RS232 to USB ports to the raspberry pi. I would like to gather information from a digital micrometer and a mercury pressure gauge and transmit it to a CNC.
There should not be a problem connecting multiple USB serial dongles to the Raspberry Pi (you will need a hub if you need more dongles than the Pi has USB sockets).
As an aside, note that the Pi has no RS232 ports. It has a UART (pins 8/10) which operates on 3V3 TTL as opposed to RS232 which typically operates at +/- 12V.
I don't have one myself, but googling reveals the StarTech ICUSB2324 should work with the Pi and provides 4 serial ports.