I think you may be approaching this from the wrong angle. It may be easier to promote and maintain one site but the real question is what are your customers looking for? I believe that multiple smaller sites will answer the needs of your customer while a larger content site can feed to the smaller sites. You might be able to group the products into three or four groups that make sense for your customers so the number of sites is decreased - and then the sites will be better able to compete for the longer tail keywords that traditionally have customers who are ready to purchase. People who type in "insurance" are less apt to buy than those who type in 'car insurance review for SUV'. Doing the research to find out what your customers are looking for is the tedious part of all of this.
I would say a little bit of both would be good. You can build one large site and the several small sites. Once the small sites are established, it would be much easier to build one of them up (then starting from scratch), if you your large site were to falter.
One big site is still my favour, too many sites are too hard to handle and maintain, for those saying you can't have different niches within the large site, ummm why not ? you can easily manage sub domains that are extensions from the main domain, have any of you tried to manage a lot of sites ? a lot of sites are a waste of time and managing them all alone is impossible. I would get the large one finished and ready, then later on if needed try to see if you can cope with a few more sites.
What about if the subject is unrelated. :: College admission internet technology business and finance Cars self help. Would you still combine into one large site? Would you do subdomains? Or create a network of smaller sites like gawker does?
Nowadays it would be prudent to go with one large site, what with Panda and multiple penalties the search engines don't want people clogging up the web with duplicates
Think of the internet just like insurance, you can make alot of money however you work to create multiple streams of income from renewals and monthly premiums. You look to close the whale but you base your day to day on those small multiple streams. In reality the internet is very similar and you can create a much safer nest egg keeping things small rather then all in one spot cuz if that deal doesn't close you lose it all.
You can have one main website with links to smaller, categorized sites. I think this is a much better approach since all of them belong to your one company. Each page in the site will be optimized for their own keywords, while your main site is optimized for your main target keywords. But I suggest you do a thorough market research first and see what keywords you need to rank for. How your site will be designed and how many categories you'll be branching into will also matter.