Manifester level is something that you choose, but it seems ... odd ... for a wilder to every manifest at less than their full level (especially when Wild Surging).
Psionic Manifesting says:
You can manifest a power at a lower manifester level than normal, but the manifester level must be high enough for you to manifest the power in question, and all level-dependent features must be based on the same manifester level.
Wild Surge says:
A wilder can choose to invoke a wild surge whenever she manifests a power. When she does so, she gains +1 to her manifester level with that manifestation of the power.
At 3rd level, a wilder boosts her manifester level by two instead of one. At 7th level, she boosts her manifester level by three; at 11th level, by four; at 15th level, by five; and at 19th level, by six. The wilder always wild surges for the maximum amount possible, for unleashing emotions in the fashion of a wild surge does not lend itself to using finesse.
So, the wilder can choose her starting manifester level, but she cannot choose how much to Wild Surge, just whether to do so.
... so, a wilder, when manifesting a power, would:
- choose power
- choose to lower their manifester level or not
- choose whether to use Wild Surge (and, thus, increase effective manifester level)
- choose target/range/effect/version/feats/... to employ as appropriate/needed
- pay power points (if needed)
- the power is manifested as the wilder wishes (barring saves, illusions, null-psionics zones, etc.)
- roll for ennervation (if needed)
Note that, the vast majority of purposes, all of the above steps happen as a single "action". Further, for (virtually?) all purposes, steps 1-5 happen simultaneously: "I cast Crystal Shards, with a lowered Manifester Level of 1, Wild Surged to ML 2, targeting the goblin on the left; having spent a power point, if I make this touch attack, he's taking 2d6 piercing damage" is a nigh-uninterruptable "event" encompassing steps 1-5, and ending with a d20 roll to determine how step 6 plays out.