For Point 1: You need CORS enabled for the service to be consumed if you want to make Ajax call from a sightly component.
For Point 2: If you are going to use WCMPojo, you should be taking cache and clear the responses and its tied to the component.
For Point 3: Create a common servlet to pass on the response code through HttpURL Connection to servlet response and read it through any component however you want it. Here again, you should be taking care of cache and clear the responses but the code is common and can be used in any component and externalize the URL you want to call in the servlet.
I will leave it to you on how you want to implement. I prefer option 3.
Decide on the approach keeping how you want to handle the request. If you write a server side code, the responses are going to get cached and you might have to clear it out before you pull in a new request or some how you have to disable the cache for the same.
If you don't need to cache , may be you can figure out to use clientside (ajax call). But then may be you have to figure out how you are going to handle the response. If it is just to display on the page a simple ajax call would do.