There is no max on the number of sensors you can have on your robot. The only limitation is how many ports you have available on your cortex. However, keep in mind that Digital Port 10 cannot be converted into an interrupt. (Documentation link below)
Depends, ROBOTC or easyC? ROBOTC dictates the ultrasonic, but not the quadrature. easyC dictates both. You can see a more detailed explanation for where they go in the help file for each respective program. (Search for “Motor and Sensors” in ROBOTC)
Correct. ROBOTC will handle all of the listening, etc. for all sensors, assuming you’ve properly set the to the right type. You can always manually listen if you set to Digital IN/OUTS where they should be something different.
edjubuh is correct, it should theoretically be limited by the number of digital ports, however, there is a conflict between port 4 and port 10 so only one or the other can be used as an interrupt. Here is one ref