Forum Moderators: buckworks
I would NOT use htaccess for those 3000 products. I assume those products are categorized. How many categories and do the categories have sub categories? If so, then you could set htaccess up to filter requests for the major categories and send them to a PHP handler that takes care of the redirects (the script can be cached). Using htaccess this way means you'll need to look for some common URI formatting that will not exist on the new cart.
Not just like your situation as you're keeping the same domain-which should make the rank transition shorter.