Make sure you have a few rounds warning when the party approaches. That way you can start summoning before they arrive so you out number them from the start, what you don't want is 4 PCs ganging up on each monster as you summon it. Summon the weak monsters first as they won't last long against the PCs anyway.
A nasty environment would be a large cave, badly lit with lots of broken ground, stalagmites & stalactites, a stream and/or a few pools of water and some holes in the ground. Several ways in and out including some in the floor. Your ooze will have a lot of places to hide; up in the cave roof where you can see everything would be the best place. Try to split the party members up so they cannot easily support each other, maybe have the Dretch as bait, have it open the attack by casting it's Scare and/or Stinking Cloud then running away across the cavern, hopefully they will spread out a bit as they chase it.
Start the real attack by summoning a Huge Monstrous Centipede (to big to hide so make it your first summons) and having the already summoned wolves charging in from behind the rocks, badgers attacking from holes in the ground and an apes (+14 Climb) dropping from above. Isolate the party members where possible. If the PCs enter water summon one of the aquatic monsters - they tend to have good stats for their level.
If you want it worse than that take the above but have the party crossing the cave on a rope bridge 15' up, then drop the bridge.
Feats (no Dragon Magazine):
1: Precocious Apprentice
Wizard: Scribe Scroll
Bonus: Arcane Thesis (Summon Monster I) +2 caster level and -1 to metamagic costs for selected spell only.
Bonus: Extend Spell
2: Cloudy Conjuration
Automatic from Ooze: Augment Summoning
3: Arcane Thesis (Summon Monster II)
4: Silent spell
6: Arcane Thesis (Summon Monster III)
6: Still spell
Silent and Still spell are to make it harder for the party to find you.
You can use the metamagics for free due to Arcane Thesis (they all cost +1).
If Dragon Magazine is allowed (for Easy Metamagic)
1: Precocious Apprentice
Wizard: Scribe Scroll
Bonus: Metamagic School Focus
Bonus: Extend Spell
2: Arcane Thesis (Summon Monster I) +2 caster level and -1 to metamagic costs for selected spell only.
Automatic from Ooze: Augment Summoning
3: Arcane Thesis (Summon Monster II)
4: Repeat Spell
6: Arcane Thesis (Summon Monster III)
6: Easy Metamagic (Repeat Spell)
Combining Metamagic School Focus, Arcane Thesis and Easy Metamagic reduces the cost of Repeat Spell to +0 three times per day, use for Summon Monster III to get an extra 3 creatures