Telekinesis on Colossal Siangham (assuming you can carry them) or Gargantuan Nunchaku (can definitely be safely carried in a Bag of Holding) or Colossal Crossbow Bolts (cheaper, but they break) is the best direct damage spell in the game, dealing 30d6 (Colossal Siangham) or 20d6 (Gargantuan Nunchaku or Colossal Crossbow Bolts) damage at level 15 if you miss with half the weapons (no save, no SR, goes through AMFs, but DR really hurts). Unfortunately, it probably won't be too long before your DM gets annoyed and you find yourself on the receiving end of one of these salvoes, so I wouldn't use it .
I mention this because it might be kind of cool to play an arcane caster who wears armor without burning a precious feat and boosting spell levels. After all, a high dex is nice, but armor really does help you stay alive.
Str 7? You're going to have problems with any kind of combat, melee or ranged. All you could really use for ranged combat without getting a penalty to damage is the crossbow .
Given that, are you sure you want to play an Elf? (Don't get me wrong, I'm all about RP, but you still have to consider your mechanics when designing a PC.) Those WPs they get will be virtually useless to you.
A small-sized race would get you a +1 size bonus to your AC, won't affect your damage output from spells, and only marginally affects your damage from a crossbow. In the PHB, the Gnome gets you a +2Con bonus, etc., and the Halfling gets you a +2Dex bonus...but both, unfortunately, also give you a -2Str penalty.
Human would get you a bonus feat. Half-Elf gets you some of the bennies of being an Elf without the WPs that you really can't use. Both would effectively let you retain Wizard as your favored class.
You need at least two hands to use a bow, regardless of its size. A longbow is too unwieldy to use while you are mounted. If you have a penalty for low Strength, apply it to damage rolls when you use a longbow. If you have a bonus for high Strength, you can apply it to damage rolls when you use a composite longbow (see below) but not a regular longbow.
Str penalty also applies to slings and throwing weapons. Using a crossbow is fine at lower levels, really. If you play a low-str mage don't skimp on the teleportation spells. I don't like relying on dimension door since it burns a 4th-level slot, but some swear by it.
As a "blaster" sorc you really want to play the metamagic variant from PHBII, so you can apply metamagic without messing up your cast times.