Having spent some time as a "Lighting Guy" your going to want no more than 2 of these on a UK circuit. If your going to be switching them on and off a lot go with the solid state relays if not normal relays will do. I would get a relay per fixture as they are fairly inexpensive especially for normal relays. I would expect that 1000w halogen floods will not be completely lit in 500ms as they take a long while to get to temp.
PS good SSR's will let you PWM dimm the lights if you wanted to just make sure it's not a zero crossing SSR.