Two opinions on the discussion here:
1) For the quest-introducer, it doesn't need to be higher level than the PC's. Anyone can introduce a quest -- a parent with a missing child, townsfolk threatened by monsters, etc. -- it doesn't have to be Elminster. Quests can also be introduced by the "in media res" method -- starting the story in the middle, with the PC's already in a party together and in a fight -- or by an item (hey, look at this scroll I found!).
1a) Power isn't level. An NPC can be powerful for political, economic, or social reasons, without having a high level. For example, the guy who runs the only magic shop in my campaign is mid-level. However, the people who trade with him are adventurers and retired mages and clerics. Messing with him is self-evidently a bad idea, not because he's uber powerful, but because the guy who gave him the Staff of Buttkicking to sell is going to be very mad at YOU if he doesn't get the money. Same goes for militia (police), minor manor holders or merchants, etc.
1b) The reason to not attack a random NPC shouldn't be because the PC's are weaklings. It should be because the PC's are heroes -- or failing that, because they aren't pyschopaths and treat NPC's as if they were people, or failing that, because they know the campaign is dynamic and killing the manor lord will bring down outlawry (inability to get any help from NPC's) and the full force of the law and bounty hunters down on them. That is -- have a campaign world and use it as a real world. It's more fun and emersive for the players than "everybody is too tough to fight". Keep the PC's special, but not too special -- they still have to live with the consequences of their actions.
2) I'd start the PC's at first level, not 7th. Especially if the players are also inexperienced, it gives you all a chance to learn the game -- and the PC's place in the game world -- rather than jumping in with too much complexity and power all at once. Start at 1st level, and you'll appreciate 3rd level, and amaze at the power of 7th . . . (in editions predating 4e, at least).