I believe it's still worth it. Using a CDN will definitely help speed up the delivery of your static assets especially to those who are further away from your origin server. They're also quite simple to set up as there are many Wordpress plugins out there that allow you to simply enter your CDN url which will rewrite your current static asset URLs (e.g. CDN Enabler).

Using a pay-as-you-go CDN service would likely be the way you would want to go just so that you aren't tied down to any monthly commitment that you may not end up fully using.

I would suggest taking a look at KeyCDN (https://www.keycdn.com/) which is quite affordable.

Depends on how much you care about your users but yes, I would.

CDN's are very cheap and easy to setup. No big contracts or commitments these days. You can use them just for the static assets or for your entire site to make it faster for everyone while also reducing requests to your origin server.

MaxCDN is cheap and effective or you can use CloudFlare and get their security features too and not worry about bandwidth.