I would get one of each because you're going to be stronger or weaker with certain exercises and you'll want to switch to the band that's the appropriate resistance. You can always use two different strength bands (i.e. a mini + a monster mini) if one isn't enough resistance.
You'd definitely want a pair of each strength band if you were going to use them for lifts in the gym (i.e. squat, bench, deadlift) though, but it doesn't sound like that's how you intend on using them for now.
As far as the second question, I have no experience with using bands for jumps or sprints, so I really can't answer that one. Sorry.