He can only maintain 5 spell effects at a time on level 19 (1 on level 1 - see Sustain Dweomer). This loophole does not exist, other than for instantaneous spells with permanent utility (I can't think of any off-hand; Creations, Runes, etc. all have duration and are thus subjected to this rule).
Anyways, I like this class although I'm not crazy about combining Invocations & Arcane Casting into one base class. The ability to use Invocations to cover the "usual crap" with arcane magic as the "oh ****"-button seems to work out pretty well.