Ask HN: Starting my first web app

Note: I tried doing a search for a similar thread but the searchyc site seemed down and doing a Google search for "first web app site:news.ycombinator.com" didn't turn much up. Feel free to post a link to be thread if this has been asked before.

I'm ready to dive into creating my first web app. Most of my experience is on front-end development/design, but I think I have a killer idea and it's a great opportunity for me to learn more about programming.

That being said I have 2 questions. I've (very lightly) looked into PHP, Ruby on Rails, and Django. The depth of my experience for ROR and Django involve installing both and making a clock program. I have the most experience with PHP, but does anyone have any advice on which language I should use? Pros/cons?

2nd question: do you have any great resources for planning my project? Since this is my first time I 'm wondering what other hackers workflows are like. Do you typically work on the app locally and getting it to work for yourself, then build in features to open it up for other users?

I'm really just looking for any helpful guidance on getting started.

Thanks in advance for your help!