I'm preparing to launch a service soon which will provide third party websites a widget. The widget requires my javascript file in the website's code. Exactly the same way services like analytics, uservoice, sharethis, getclicky, etc provide you with a javascript snippet to add to your page.

Therefore, my javascript file is going to be hotlinked by tons of websites which possibly receive a lot of requests too.

I need advice/opinions on the following aspects:

1. What's the right location for hosting this file? Should I use a sub-domain for it? I was thinking of something like http://api.myservice.com/js/foo.js . Remember, once websites start embedding this file, its location CANNOT change under any circumstances.

2. Right now we can afford just one dedicated server. So I have minified my file, enabled gzip and plan to use some good cache control headers through apache. Also, in the near future when the requests pickup, I will use a http proxy like Varnish. Is this a good plan for the near future?

3. Should I be considering a CDN in the future (since we can't afford it now)? If so how do I make sure we're prepared to migrate to it without breaking services. Pros/Cons of moving just this file to a CDN? Also, since its just one javascript file(50kb), any affordable CDN so we could consider it in the beginning itself?

4. Any other word of advice I could use? Anything I shouldn't overlook at this stage which I would regret later? (both in terms of server + javascript ajax limitations)

Thanks in advance.