back in my shukokai days I was rather fond of sweeping.
However I always used my front leg against their front leg, inside (sneaky and causes them to go 'dead' weight) or outside (full takedown). this was training geared towards semi contact of course.
I have to admit that I now dont train for sport therefore my sweeps are far more aggresive stomps or 'cutting' kicks to legs. i think the practical side of many sweeps is questionable in a self defense situation in general.
Haha, as a "Brit", I can certainly confirm a good 3.) I dont often use as a full take down though, just a tap to unnerve balance stepping through with a strong gyaku zuki. And theres no reason why it has to be from the "rear" leg...