If it is not practical for an open site inspection I have no problem on sight wells. This is a case by case basis. If there critcal issues with like bedding or compacting then sight well may not be the way to go. Same applies with the number of wells.
As far as where they would shound be placed, I would recommend above the buried conduit(s). If they were on the side or underneath the conduit, it would sort of be a mute point. All kidding aside, It is all a case by case basis. I think there are too many varibles to figure on to give a rule of thumb answer.
John is correct when he says to call the AHJ before starting any work. It is much easier than digging twice. I have people tell me all the time, "I took pictures!" The problem with that is after awhile, all the trenches look the same! I don't even look at pictures anymore. I would rather they use the sight pipe and back fill area that are critical for moving cars and machinery around the sight. Places like parking lots and condos where the trench is in the road, it would be to dangerous to leave the road open.