Electrical question.

I'm redecorating the sitting room and it has all white plastic sockets,
light switches, aerial points etc. I'd like to replace these with metal
faceplates.

1. Is this a job that a reasonably competent d-i-y-er could take on? I'm
assuming that the wiring schema won't differ? Will this hold good for
dimmer switches as well?

2. From what I can gather, the fixings for the faceplates are at the same
centres, but are the screws/threads likely to be the same? Or will I need
to change the boxes as well?

3. Are all faceplates for sockets/light switches the same, or are they
sized according to the depth of the box behind?

In other words, what do I need to do/measure to be able to change like for
like?

Thanks

Edward