Lets say during interfacing, im controlling my whole hardware side including a PIC by means of serial port, but my laptop has only USB, if i use the USB-serial converter cable, would it affect anything when im getting the results from the hardware? What about when im writing the coding to read from the serial port, do i write the code like im controlling the serial ports?
Yes you can. That serial port will appear and behave exactly as a normal port, exept there might be a problem if you bit-bang the controll lines (eg if you use it as a primitive paralel port in software.). Normal serial activity is not affected.