Even though they should be well within or on the verge of Paragon tier (7th level is 35% of a max 20th level campaign; 35% of 30 is 10.5) I would seriously consider making them lower than seventh level.
First, because as it has been suggested above, this gives them time to get used to the system.
Second, because I get the feel that characters can do a hell of a lot more in combat in 4e than they could at an equivalent level in 3e.
I'd say try level 5. If it's too low, then you can always speed up the XP gain a bit after trying it out.
It's much easier to aim low and move the PCs higher if it doesn't feel right, than to aim high, make them higher level, and then realize you should have gone lower.