Founder of CourseCraft, Bugrocket. Maker of many weekend open-source projects. Occasional tweeter and blogger.
As a long time Rails developer, I'd say the accepted gold standard for file upload hosting/etc is Amazon S3. Storage and bandwidth are both extremely cheap and reliable. You might look into 'carrierwave' to handle the uploads and URL generation more smoothly. You can also setup direct upload to an S3 bucket from the users browser (via CORS), check out 'carrierwave-direct' for that.
I worked on a prototype of an application with similar needs but focused on furniture instead of apparel. Unfortunately it was pretty tough going. The best data we found was through sites like Commission Junction (now 'CJ Affiliate') and ShareASale. These sites also have apparel data, some of which I saw during the process (since during testing I didn't really mind the type of products).
The data we got from them is quite a bit like what you've described, but it's hit or miss when it comes to accuracy. Their 'API's also leave a lot to be desired, we ended up having to build some FTP fetch-and-parse type systems to deal with each provider and update our own dataset.
As of this writing the latest version of PHP was released a mere 21 days ago -- certainly nothing 'outdated' about it!
My advice would be to not worry about the latest/greatest/most hyped up new thing, and simply go with what you know. You can make serious progress on your product much quicker if you stick with a stack you're already comfortable with.
I say all of the above as someone who doesn't really like PHP, too, for what it's worth -- choice of stack is much more about personal preference than any objective measure of what is 'best'.