If you want to worry about dark side, I think a focused practitioner has a lot going for it, because of the laws of magic. If you don't want him to be a typical "lore/discipline/conviction" guy you can use stunts to shift key skill trappings around (it's easier if you stick with Channeling or Rituals, rather than trying to do both). There's plenty of precedent for someone with latent talents getting a power boost by being near a big magical event. (eg, some college student who got too close to the Darkhallow having talents awakened either for necromancy or its opposite)
Consider a speedster whose power is based on having time go slower around him, rather than kinetomancy. You avoid all the issues of tearing yourself apart (the world is slow around you, rather than you being super fast) and what you can do is different (you don't cause sonic booms even if you travel objectively at speed of sound, but your ability to communicate is challenged...everyone speaks so sloooww, and you speak really fast and you can probably search a room really quickly without causing a vortex of wind to blow everything around).
Such a speedster will be right on the edge of the time travel Law, might even have Lawbreaker feats, and if you have rituals you're likely to be able to actually capable of time travel, maybe even opening time-travel "ways" for others even if you don't for lawbreaking reasons.
Even a typical "flash" type build has risks of first law violations (you hit someone too hard, or your slipstream-fallout causes property damage to the point where somebody dies). Some kind of aspect indicating you're addicted to speed could work nicely with a feeding dependency to encourage you to use your powers and then pay for it later.
By contrast "Emissary" and "I'm a creature of the never never" type concepts tend to be less conflicted. You behave according to your nature, or that of your boss...the problem is not as personal.
Mechanically I'd do the speed-addicted Kinetomancer as a channeler (area punches/maneuvers, rapid-fire punches for high shift single attacks, blocks where you catch all the bullets/knives/block punches within a zone, etc with options on sonic booms, slipstreams and similar effects where appropriate or for fallout) and the chronomancer/lawbreaker as a ritualist (magic items or potions for combat-speed effects, normal rituals to let you do things like search an entire building in 15 minutes or read an entire library in a day). Frankly the speed-addicted kinetomancer sounds more like a typical superhero of the two examples, but there are some more cerebral superheroes out there, and a contrast between his greater power (slow rituals) and the desire to just go "fight crime" and do flashy hero things might also be entertaining...high concept vs trouble kind of stuff.