is osCommerce scalable?

You want to invest in osCommerce but you want your site to last the distance. Sure you can keep it up to date in terms of design and technology such as the latest versions of php and MySQL, but even if you do, can it really cope with large product catalogs and high order loads?
The quick answer is yes it can. We have sites with product catalogs of up to 20,000 products. We also have sites taking 100 orders an hour. And what did we have to do to osCommerce to support that? Answer. Nothing.
Scalability becomes a hardware issue long before it would ever becomes a software one.  You cannot run a serious eCommerce store on shared hosting.  You need a dedicated server and for that you need to budget about $350 a month.  With its own sever to run on, osCommerce performs like a champion.