“So for hardware questions. If I use a ribbon cable and snip the 5+ lines but leave the rest this should be sufficient?
Yes that’s fine. Just be careful with the wiring. The current OSPi uses the design where RPi plugs directly into the female pin headers on OSPi board. As long as you follow the same wiring, you can use ribbon cables to connect the two without plugging them into each other.
Another option is to make use of the pinouts on OSPi: at the top edge of the OSPi board. all 2×20 pins of RPi are mapped out. So you can solder pin headers there and connect other components to whatever GPIO pins you need.
“Can the different zones be controlled seperately? ”
I am not entirely sure what you mean. At least you can set up multiple programs if you have a fairly complex watering schedule.
About port: yes you can change the port to other than 80 or 8080.