What kind of interface does your 7-segment display have ?
If it's discrete, then you typically will need 4 outputs per digit, as the 7-segment display will have a BCD to 7-segment decoder chip inside. That's a lot of outputs to use to drive a display.
If it uses Modbus RTU (serial) or Modbus TCP (Ethernet) that will probably be easier.
Many "7 segment displays" are actually panel meters, with an analog input.
Describe as much as you can about how the 7-segment display you want to use works.