3.5 Questions about magic at low levels (breaking max cap level on skills/metamagic)

[Isiloki]

Hey there! So I play a Wu Jen, currently lvl 6 (No multiclass in sight for now)
I'm going full spells mode (yes, I know about Body out of body but I don't want to go gish anyway), and I have some questions.

1/ Wu Jen have 1 free metamagic feat at lvl 1, and kind of a free metamagic feat at level 3 with their class ability spell secret.
Spell secret : Enlarge Spell, Extend Spell, Still Spell, or Silent Spell without modifying the spell level
What are the use I could make of that, because I just can't see it. Any idea on the metamagic feat to pick up?

2/ I'm looking for ways to break the cap spells have with max damage.
A fireball does CasterLevel * d6, max 10.
Is there a way to bypass the "max10" and deal 12d6 if my caster level is 12.
There are 2 feats I know about that are Reserves of Strength (max +3) and Cali****e Elementalist from 3.0 edition.
Any idea?

3/ I've read a lot about wizard itemization since Wu Jen is a lot similar, but apart from the headband of intellect (+2), I couldn't find anything really useful

Thank you!

[Troacctid]

1/ Wu Jen have 1 free metamagic feat at lvl 1, and kind of a free metamagic feat at level 3 with their class ability spell secret.
Spell secret : Enlarge Spell, Extend Spell, Still Spell, or Silent Spell without modifying the spell level
What are the use I could make of that, because I just can't see it. Any idea on the metamagic feat to pick up?

Extend is great to pick up on buff spells, or other things you want active for a long duration. It's particularly helpful at low levels, where your CL may not be high enough to produce a long enough duration. For example, at 3rd level, you might choose extended rope trick as your secret so that it can last a full night's rest at 4th level.

Still Spell is notable for letting you cast spells while grappled (if there aren't material components); similarly, Silent Spell lets you cast spells while silenced. They're good for spells that you want to always have access to, even in uncomfortable conditions. A silent dimension door has no components at all, so it's very hard to stop you from casting it, making it an even better panic button than usual.

Enlarge Spell mostly comes in handy on spells with close range (i.e. 25 ft + 5/level), like those scarves Wu Jens always seem to be tossing around for some reason. It can give you the space you need to stay out of an enemy's charging distance.

For the free metamagic feat, it's mostly a good chance to pick up prerequisites. Lots of prestige classes require metamagic feats, and lots of the best metamagic feats require you to have other metamagic feats. (Invisible Spell or Sculpt Spell, for example, would be great choices, except you can't choose them on their own.) If you're not going to focus your build around metamagic, you could pick up something like one of the Sudden metamagics just for value, I guess. If you are interested in actually making use of metamagic via Arcane Thesis and the like, Empower Spell and Fell Drain are pretty good choices.