I have already searched but didn't managed to find a suitable answer.
My problem is this: I use different software packages with different licenses to develop a free and open-source (not commercial) piece of software (a simple data visualization web app that reads data from a specific mysql db and draws graphs and stuff) that I want to release to the public as well.
It all started with me writing some simple PHP code using a chart drawing library which is under the GPL. That was the initial version that I simply released through by blog without any license notice.
On the next stage I integrated the results (chart images etc) within a free web template from os-templates.com which comes under a license of their own (they simply say that they allow usage for non-commercial and commercial projects with proper attribution to them, fine by me), in order to have a nice looking presentation/interface for them. I released that updated version without any license as well.
Next, I expanded the script by using a google visualization api library which is under the BSD license to draw some additional google maps/charts. Still no license notice on my new release.
I now want to continue working on this project but I think it's time to license it under an open-source license because it's getting bigger and bigger.
Do you have any ideas at all of how can I do this? My work is the php code I wrote and all the other changes I have made to the template (html/css). Must I license it as a whole? Or can I just say that so-and-so libraries and other stuff included have their so-and-so respective licenses, while I release my code and only that under a license of my choice?
Any suggestions would be nice.
Edit: By the way, I know that "discuss it with a lawyer" can be a common answer, but we're talking about a small personal/hobby project that due to its nature (application-specific) no more than ~50 people will download/use (ever I guess). So I'm mostly looking for an easy solution, not something complicated like consulting a professional (and pay for it).
Edit 2: Something else I want to note so there won't be any confusion is that apart from the template which I altered for obvious reasons, I just use the libraries' API by calling their specific functions etc. I haven't build upon them or altered them in any way. I'm saying this because as I understand it, building upon and extending an existing open source project is considered making a derivative and you should follow specific licensing guidelines (eg release the new code under the same license). In my case I just use the libraries as-is, nothing more.