As some of the others have said, add up all your light bulbs that will give you your total wattage at max output, most dimmers are rated at 250w and 400w, if you going to get another dimmer then make sure it is capable of taking max load of the light bulbs. However if your going to do away with the dimmer and just use a switch then theses are rated in amps, normally 6 amps which should be sufficient, If my memory serves me right i think the company MK rate there switches at 10 amps.
Dont buy a shit quality switch, spend your money and get something like an MK one, diy stores own stuff is shit. What we mean when we say is it one way or two way is if you walk in one dorr and turn it on can you walk out another door and turn them off? if so thats 2 way and you need to make sure the switch you buy is 2 way (it'll say on the packet).
As for turning off the electrics do it from the fuse board. on the circuit your planning on working on.
Richie