You will need one run of cable for the PIRs, and one run of cable for the lights, both runs led back to a junction box.
The PIRs have pretty weedy contacts, so I would consider using a contactor to alleviate the large load on them and extend their lives, and since most PIRs have a maximum rating of 1000-2000 watts, this is also a nessecity if all PIRs will control all lights.
And you dont need any ring mains. Lighting isn't wired as ring mains.
I am going to advise you ask an electrician to do this work. It will require a new circuit and is outdoors, and as such, is notifiable to your local council, which your electrician will take care of. Outdoor electrics require special attention, due to their location. Electricity has no prejudices, it kills anyone.
Also consider your neighbours. Make sure your lights dont shine into their gardens, or over your fences, or onto roads etc. And ensure your PIRs are adjusted so people walking around next door's garden / along the pavement wont trigger your lights.
And one last thing. You may have up to 1800w of lights there. They may "just be lights", but they use a heck of a lot of power. Consider instead, a few "lantern" type lights with 20 watt energy saving lights in, on a timer. Or downsize the halogen lights to 150 watts.