You start to configure when either ATC tell you to
Yeh, right. Who told you that?
We will have worked out our approach (strategy) in the approach briefing - one of us gives the briefing but its a 2 way thing.
We look at the approach and the met and w/v and the condition of the aircraft and weight alt temp considerations runway length any considerations of the runway and surrounding terrain, traffic, everything - under alt will come MSA - we will also look at how we are going to do a go around should that be necessary for any reason - like a herd of elephants crossing the runway just as we are about to land, that sort of thing.
Depending on traffic, time of day, atc >> traffic, time of day, we expect, ideally to do a seamless approach to intercept the glideslope (guidance in elevation) and the localiser (guidance in azimuth [right or left]) or Instrument Landing System or other type of precision or non precision approach or visual approach.
We know and get used to our aircraft but, we have charts which will help us to make a decision as to what speed we will be at by a certain distance from touchdown.
For example if we are constrained to be at a low speed earlier on in the approach then we would configure earlier, depending on that speed.
Approaching over sea coasting in to an airport over featureless terrain and no obstacles which is also flat near sea level with few if any population and with no traffic around we might descend from cruise straight to 2,000 having planned this way back up there at cruise altitude, to be level by 2,000 feet say, then cleared down to say 1700 feet with no speed restriction and using slight reduction in rate of descent to decrease speed and as we pass a certain low speed say 180kts for example then we would prepare for lowering one stage of flap. Leaving 180 decellerating would call for flap 1. Decellerating further flap 2 aiming to have flap 3 by 160kts. At about one dot below the glideslope meaning just before we are fully established on the glideslope and descending with it, we would select gear down - another way of looking at this is, instead, distance from touchdown, so you could say at 4.5 miles select gear down and full flap - for example - So overall it is usually based on distance (from touchdown) and altitude but moreover - speed as to when you configure.
If we configure too early, after having got the speed back then we end up dragging the aircraft in on a slow approach with high power settings and loads of noise, if there were traffic behind us then we would be holding everybody up and the queue would not be appreciated by pilots, controllers and passengers alike, who would be awful
off at losing their connecting flights . . . also we would use more fuel that way.
If we configure too late then we run the risk of not being "stabilised" by a certain altitude, at some airlines this is 1,000 feet - at others it may be different - in this case we would have to go around.
So all in all we configure by a certain dist from touchdown, a certain altitude and, a certain speed -
we decide when to configure - not ATC.
Re: your last question - we decide on whether to land with Flaps3 or 4 by consulting the flip card which will have the weight of the aircraft, outside temp, we select the appropriate card where the figures all match up and it will give us its recommendation. Should we decide that Flaps 3 is not enough for any reason and that, indeed, Flaps full is more appropriate then we would select Flaps full.
Also how do you judge reverse thrust i.e reverse 1 or 2 and maybe no reverse just brakes?
We would not have Reverse 1 or 2, if we could help it - the only time this would happen is if reverse 1, or 2, was inop, or if landing single engine but we try to avoid asymetric reversers if possible, you can imagine why.
We would use brakes with no reverse if, we were light and did not have to land and hold short or take an early turnoff or we had to / could roll right to the end of a long runway, in other words if we did not have to slow quickly or use brakes too much . . . there is little point in foregoing reverse but end up burning your brakes . . .under certain conditions we cannot use reverse.
We can land with autobrake minimum or medium, again it depends on condition of aircraft, heat of brakes, weight, temperature and length and condition of runway available.