as far as spells getting interupted that has nothing to do with m.acc

There are three situations that will cause a spell to be interupted

1) Selecting the spell a second time while it is casting (if you have that option toggled on in the game config)
2) Movement. If you move the spell will interupt that includes being buffeted around by monster abilitys with knockback.
3) Damage. If you sustain enough damage while the spell is being cast you will be interrupted. At the moment there are few counters. The chief among them being well.. not taking damage while casting. The cc spells sleep and blizzara can and will buy you the time and space you need to cast. Out side of that Sanquin will make you immune to spell interrupt from damage.

Sanquin is the Oh shit button in the thm/blm arsenal. And it has saved my sorry rear more times then I can count.