Personally I'd prolly have Hob, Down Ring, Up ring, Immersion heater (if you have one), Up lts and Down lts. I think If you're gonna run a 2.5 to every socket anyway you might as well chuck the last leg in to make it a ring for the time it takes.
If you do use a twin RCD board instead of RCBO then you want Up sockets on the same RCD as downstairs lights and vice versa. This way if you plug summat in upstairs which trips the RCD then the lights are still on.
Another thing I do is have a non RCD lighting circuit in the mains cupboard, if there is one, so thats always gonna stay on.
Dunno why anyone would use 1.5 t&e for a lighting circuit pulling about 1 amp. Use 1mm its cheaper, easier to terminate and easier to pull in.