Well, your build idea won't work. Loremaster isn't enterable until after level 7 due to skill point requirements.
More info would be great. What books does your group have available? Divine Oracle is a really good class for a wizard to take before entering Loremaster, and it gives you an ability that is nearly identical to Evasion, and access to a bunch of neato Divination spells.
If you have Complete Mage, I'd highly suggest something more like this:
Focused Specialist Conjourer (banning Enchantment, Evocation, and Abjuration), and focusing on utilizing cloud spells, debuff spells, and various teleport spells to influence the battle. At level 3, you would probably look like this:
Focused Specialist Conjourer1 Extend Spell, Sculpt Spell, Scribe Scroll
Conjourer3 Metamagic School Focus (Conjouration)
And your spells, assuming an 18 starting int would be
*Sculpted Grease (using MMSF)
*Benign Transpostion (in Spell Compendium)
Ray of Enfeeblement
* Scupted Glitterdust (using MMSF)
* Sculpted Glitterdust (again, MMSF)
With the * spells being required Conjourations due to Focused Specialist.
The key is to try not to use very many spells per combat. 1-2 should be enough to cripple your foes badly enough that your party can kill them easily. Especially Sculpted Glitterdust. That'll be a killer. This low level build will really make you effective in the party, although your friends will all think they are doing all the work (this is the Batman style of play). Glitterdust is AMAZING, since its a multitarget Blindness, and blinding a foe is almost like casting Greater Invisibility on your whole party. Thats awesome.
Don't go Mystic Theurge. You touched on all the reasons its bad. The worst is the 3 level loss. Thats just inexcusable for any class that claims to be a "primary caster".