Your current camera is more than good enough. A better camera will not make a noticeable difference.
You should probably get Canon 24-70mm f/2.8L and 70-200mm f/2.8L IS first (about $2500-$2800). Then, get some flash/strobe lights for portraiture (from a few hundred to a few thousand dollars). And a tripod, a few memory cards. If there is money left, get a computer with large RAM and fast harddisk drive, and Photoshop CS2.
Luckily the tripod, several memory cards, and CS2 are already in hand. Thought my computer had enough memory until I got the 350, but ah, well...
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