Leopard WebKit is more updated than Safari for PPC (Version 5.0.6), but TenFourFox has the most support. Do yourself a favor and use TenFourFox. To ensure you get an optimal web experience you are going to want three things. TenFourFox (Latest Version), MacTubes 3.1.6, and MacTubes Enabler.
Get everything setup and install both MacTubes and MacTubes Enabler. Then fire up MacTubes and go to Preferences. Set the video player to QuickTime Player. This will prevent Flash from being used and also play videos in a better format for a G5.
As for video and photo editing. iLife is a good place to start for beginners. However, old copies of Photoshop and Creative Suite can be had for pennies compared to the newer versions. The best it will run is CS4, but CS2 can be acquired much cheaper. Final Cut Pro will run officially up to version 6, but a hack can be used to get version 7 going.