Easy question first...I think Provoke makes more sense for your character. This isn't just because Harbringer is using Empathy and will. Based on what you've talked about so far, Provoke implies the "forcing someone to do what you want" approach you seem headed for. But choosing your final Powers or Aspects might alter something.
So, on Stunts and Powers. The "by the book" answer is that you should have 3 refresh left over when you are done. That is not mandatory though. When you play Fate in a face-to-face game, you get a number of Fate Points equal to the number of Refresh that you have every time you sit down for a new session of play. (3 being the typical number) Since we are playing online that won't work. I will probably be telling you "refresh" you Fate Points every 3-5 scenes depending on how intense they may have been or if you advanced the plot, or if there is a time jump. **Note: If you end a scene with more than your Refresh number you will not lose Fate Points, you just don't get any more at that time.**
Stunts are trick or things that your character can do that make them special and set them apart from other characters. You've seen how each skill offers a few (3?) examples of stunts tied to each skill. Some require the spending of Fate Points some only trigger under certain circumstances but don't cost Points. Powers are effectively the same thing in our game, but rather than being related to Skills, they represent the superhuman abilities your character can have. In the Venture City Stories it gives several examples of powers. The Speedster can move 3 zones in a single move at no cost of a Fate point. Normal people can move one zone, two maybe with a skill check. **Note: Zones represent various areas in a scene. Typically you can only affect things in your current zone. Punch a gangbanger, pick up a trashcan, etc. Ranged attacks obviously improve your area of effect in accordance with their nature (a gun or whip, or a lighting bolt). In this game, I imagine a typical zone to be about half a city block, or two building lengths, but it could vary depending on the situation. Think about running across a room and punching someone in a short amount of time, i.e. one round of actions. However far a normal person might concievably be able to get and do something.**
Let's look at Superman for examples. For my example I will put forth that Supes has one power set. Let's call it "Kryptonian Physiology". In this set Superman typically gains the following abilities (he gains and loses powers depending on the writer, this is the traditional list) Flight, Super Strength (probably at a +6 or +8 in my opinion) Super Speed, X-ray Vision, Heat Vision, Ice Breath, and Invulenerability (Armor 10, as I would judge it).
So, by my estimation Kal-El would need 13-14 refresh to get all that. And he would be unplayable because you can't spend your refresh down to 0 in this game. You have to have one point. His draw back is huge because...I mean come one. Kryptonite kills him in minutes. Seems fair. He probably has a tone of special effects, I don't list Extra Damage among them because his strength is so high, he doesn't need the help.
The Flash on the other hand also has one Power Set, and probably just one power, Super Speed. You could throw on things like Whirlwinds and Phasing through walls, but in the way I would build him, those would be special effects. He would need to roll Athletics really well in order to pull those things off. So Flash would be at maybe 4-5 points. However, he also has crime solving skills. As a CSI he can analyse a crime scene in ways normal, untrained people can't. That could be just a Notice Skill check, but it could also be a stunt that provides a bonus to Notice rolls becausehis ability is beyond what normal people can do, but it is unrelated to the fact he can move so fast.
So, make up a list of what Warp can do with his powers and any special gifts he has that arent because of the powers, and don't worry about the cost. After we see the list we can determine the refresh cost and makes adjustments.