The only script that I know of that will do both TGP and traffic trading is Choker's Total Traffic System:
http://www.totaltrafficsystem.com/
You should be fine to use that if you just want to learn the ropes.. but as your site grows you would definitely want to invest in something better and you might have a hard time switching your system over.
Free scripts take a percentage of your traffic as payment, and they're usually lacking a lot of important features.
Right now I'm using my own code to handle the TGP aspect of my sites.. but I'm looking at purchasing something better. I've used Auto Gallery SQL on a friend's site but it's template system isn't powerful enough to do what I need.
Comus will do what I need but it's not worth the $200 IMO. I've got the free trial (which skims 2% of your traffic) running on a test site right now. The admin interface is god aweful and it's got some major bugs. The cropping tools mess up a lot and the auto scanner doesn't see recip links on galleries for some reason (both known problems .. they're just not getting fixed because the guy who maintains it is overworked and underpaid).
The Comus guys really need a designer to come in and give the admin interface a face lift .. and someone to handle support issues so Tony can work on stabalizing the code and make it a really great script. Until then I think I'm going to keep looking for something better.
As for trade scripts, I recently invested in ATX. Right now it's $250 and it's worth every penny. The two big players, up to this point, have been TM3 and UCJ but, from what I hear, ATX really stacks up against both... and the site I've got it running on is growing extremely fast since I switched from AT Lite (the free version). You can check out ATX at
http://www.arrowscripts.com
Aside from that, keep in mind that the design of your site will have the greatest impact on it's growth. If it loads too slow visitors will bounce off. If surfers don't like the content, they'll bounce off. If you concentrate on converting traffic rather than building it you won't grow much etc.
So don't get too caught up in what scripts you use. Get what you can afford and what other people say is good.. and good luck
