I would go with what you're familiar with and what you can maintain. If that is Java then great. If that is PHP then great. If that is CGI and Perl then, well, I guess that is great too though we did start a new millenium a while back
But the key isn't that Java is better than PHP is better than CGI. The key is to do what you
know. If you're going to be writing and maintaining the site then you are going to be much better off doing something you know. Trying to learn PHP while developing or maintaining a large site will just take longer.
As far as which app server - again, go with what you know. 5k hits/month is only about 7 hits per hour - not exactly big time. I've built sites with Tomcat that handle hundreds of times that volume so that isn't too much of an issue.
Database - same thing. Do you know something like PostgreSQL? Fine, use that. You are unlikely to want a commercial DB here as because of the cost but pick something you know.