I can't say definitively, I'm pretty sure you must have a break away chain or cable, to stop the trailer galavanting off down the road if it comes off the hitch. Looks like you already have one on that trailer. It's supposed to be attached to the vehicle by another point, not just looped over the ball.
Lighting regs should be easy enough to find.
You may want to consider you hitch weight. Your ball will be rated, probably 100KG. You may find the rating in the car handbook.
If the trailer is loaded, there must be weight on the hitch, but no more than what it is rated for.
You could easily exceed it with a load of fuel in the wrong place.
This is static mind, not when the vehicle is moving.
Truthfully, the chances of getting caught out by the law on that one are pretty slim, I'd say. Bit different if your towing a couple of tonne, or commercial. Then the ministry get a bit more interested.
I can't think of much else. Number plate, plus light, if you really want to be fussy.
You can get little plastic outriggers, so you can see a narrow trailer in the mirrors. Makes a heck of a difference when reversing, or even going down the road, to be able to see the trailer.
