the only way you'll find out what you need on a roadtrip is to start driving down the road.
start developing with javascript on the html page. the more in depth your page/site becomes, you'll hit a ceiling with javascript. you may need a database, or logins, or maybe you want custom form contact pages instead of the "send email to me@yahoo.com"...
then you'll need to start developing server side functions. i prefer perl. i haven't encountered a situation it couldn't handle. I bought a book for $19.99 and never looked back.
a good example of the need for server side scripting is this forum. when you submit a post, the post is parsed server side, and stored in a database (i'm guessing, but more than likely)...that way other people, like you and i, can access the post and also add to it. but look at the button that you click to submit that post...that's javascript in action...its strength is user/browser interaction (buttons, pop ups, rollovers) and organizing user influenced information for the server to receive (forms).
the best programming step i ever made was learning server side scripting. most websites are designed around a main template that remains the same (the landscape) and only the content (information) changes. before learning perl, i created individual html pages for a home page, contact us, about us, site map, store page 1, etc...i had 30 pages, and each time i made a correction to the landscape, i had to alter each page. server side scripting allowed me to have one page, like index.pl and then manipulate the content using name/value pairs (the things that follow the ? in a url)...instead of having a home.html page, i now could use index.pl?a=home and then (server side) ask what the value of 'a' is, in this case 'home' and apply the home content to the template, then serve it out to the client/browser. 1 page to edit, less headache for me.
just relating my experience. good luck.
hope that helps.
- g