Hi, one benifit to using charcoal is because the charcoal touches the crucible, and transfers heat more effectively. So you wouldn't really want to hold the charcoal off of the crucible with bars. Not to mention that if you get the charcoal hot enough those bars aren't gonna take it for long (the bars would need to be made of a refractory material).
I have a small charcoal furnace and really it is easy to use in my opinion, and usually even after I take out the crucible the charcoal pretty much stays in the shape it was while it was burning (it does not cave in right away) unless I bump it around a lot anyway.
I personally like charcoal, even though it's dirtier to handle, because it's simple, and less hassle to set up, and it gets very very hot.
You may be able to get away with having the crucible above the charcoal, but you would need a very insulated furnace to help contain the heat better, since charcoal itself is "self-insulating" you usually don't need insulation, you just need refractory lining. If you moved the crucible up you would now need insulation. Not to mention that for charcoal you need good airflow so a lot of the hot air is going up out the lid cover vent - it still seems to work best to have the crucible buried in the charcoal (look at cupolas which melt iron - the iron is actually sitting ON the charcoal or coke - no crucible at all!) but you could try it if you want to see if it would work out.