Which custom firmware should i choose?

On a linksys router i gained some experience with router modding with DD-Wrt.
Yesterday i got a wl-500g, first I want to instantly sell it for some quick cash but after a quick google search i saw that it was able to run custom firmwares.
Because the linksys doesn't have an usb port i think this lille old fellow is a nice replacement.

I like the interface of dd-wrt but i heard something about it not supporting usb functions.

My main goal:
Normal router without usb stick.
When usb stick is put in it automatically starts downloading torrents/usenet.
Controlled by some webinterface.
Know there are lots of sources out there, combined with a little c++ and php knowledge i think this is a fun little project.

Which firmware should i choose?

Your wishes are hard to fulfill. Your router has only 240 Mhz, 32 MB RAM and no harddrive. Without swap, thats not enough for torrent/oneklick/usenet. And if you switch on swap on a usb-stick, it will break sooner or later, since there is a wearout. I would stick to a usb-hd constantly plugged into the router.

Best firmware in my eyes is Olegs http://code.google.com/p/wl500g/

Install it with this HowTO: http://wl500g.info/showthread.php?t=10307

About USB wear out, I have my WL500gP with the whole OS/firmware on USB including logs and swap. It took three years before the the partition where the logs were started to fail. I just stop using that partition and created a new one. At that time I paid 15€ for a 1GB Kingston USB. Today I get a 8GB Sandisk for the same price.