That's the concentration check to do the casting, from the top half of the box. You're only casting once. If you cast a whole pile of Concentration spells and try to maintain them all simultaneously, then you're looking at some very high EF's from the "maintaining another spell" on the bottom of the table.
But the energy put into them is the total energy for all the spells. So if you keep rolling below the level of the spell, you have to dump in lots of Fatigue levels to power all the spells in total.
Yes, but note that your example above doesn't work. In one round you can do one regular cast and one fast cast, or you could do a pile of fast casts, but not one regular cast and a pile of fast casts.