Requirements
Spells: Able to cast 2nd-level divine spells and 2nd-level arcane spells.
My understanding is that Spell Like Abilities do not count as Spells and cannot be used to meet the prerequisite for the prestige class.
I've had several fun builds with this. Of course you don't have to take it as soon as possible. You could wait till your fifth level Wizard Feat and be off a couple caster levels or whatever class feature you want to grab from the class tree before switching.
One of my builds was a Sorcerer (fey)/Oracle(Waves)who was a pirate on the Inner Sea. It takes an extra level of each class to qualify but both are CHA based casters so you can jack that skill up for bonus spells and higher saves. This guy was surprisingly adequate in combat as well. I referred to him as a "second line" fighter and gave him a Long Spear so he could stand behind tanks and threaten the same squares. I went ahead and sprung for Extra Revelations to get more Oracle features while advancing in Theurge. Sure I gave up other feat options but it's always a choice and I liked how this guy turned out.
With spontaneous casting for both lists I could really just pick whatever spell I wanted. Quicken spell of course let's you cast two spells. And if you play through tenth level of Theurge and get Spell Synthesis you can theoretically cast three spells in a round. A quickened spell followed by a Divine spell simultaneous with an Arcane spell.
One of my tricks was the Water Sight Revelation which allowed me to see through mist or fog combined with Obscuring Mist (Or at 14th Level Cloud Kill and a necklace of adaptation.) Poke and move with the Long Spear. It was a blast.
I also had a +2 con bonus, Toughness and was a half elf adding hit points for two preferred classes to help make up some wherewithal.