Wiring for new storage heaters

[beinerts]

Hi all, I'm looking for some advice on installing two new storage heaters in my split level, 2 bed flat. I'm on economy 7 and have a sotarage heater in the 1st bedroom (upstairs) already which is fine. I'm installing another storage heater in the 2nd bedroom (also upstairs) and a third in the living room (downstairs). The two new heaters are to replace an ancient warm air heating system, centred upstairs. I'm going to get a spark in to do the connection at the fuseboard, but will do the donkey work myself. I've just got a few questions:

1) Can I take the economy 7 cable currently connecting the warm air stack under the floorboards to the new upstairs heater? It would reach the new heater location. It's 2.5K so the cable would be fine (sparky may have to change the fuse)

2) The floor downstairs is concrete, so I can't lay a cable under the floor. Is surface mounted trunking adequate? It would need to be 2.5mm I think for this heater, as it's 3.4 KW. Or can anyone recommend that "fake" skirting board the allows you to lay cables in it? Any other suggestions?

3) I assume I'm OK to connect the cables to local switches and connect the flex from these to the heaters? bearing in mind the sparky will come round to connect at the fuseboard and check it all.

4) Any other suggestions/things to bear in mind?

Thanks all...