Try giving
Pro Racing a call. His kits are made up from Leonelli (ie same as Gas Gas) components - prices are reasonable, and he should be able to send you a professionally put together loom that you can just plug in to the bike. Indicators are not necessary to be road legal in the UK - I wouldn't bother with them for greenlaning.
I'm also running an '06 EC300. I have it set up so that the ignition circuit is entirely seperate to the lighting. That way, it is easy to remove all the lighting kit so that it doesn't get damaged when racing. I put connectors on the hydraulic brake switch on the rear master cylinder, so that there is no need to bleed the brake when removing / refitting the lighting.