If you have steam open, simply click on the profile which you would like to view from your friends list. The steam ID will be in the url that appears in the steam browser.
If you only know the steam username, you can use steam ID look up sites like STEAMID I/O. For this website, you will want to use the steamID64 number.
Great question, I will get back to you on that one.
Contrary to popular belief, Java is not a terrible language. For this project I needed something that was easy to work with a Gremlin database -- the tinkerpop framework makes this very convenient. Overall, I needed a backend because I cannot dish out my steam api key to users. Plus, this way I can cache steam friends making graph creation times faster.
Since the server caches all the friend requests in a local graph database, it is possible to not see all your friends if you recently added them. I am working on a solution to this, however, I don't want to excessively hammer the steam API if I don't have to.