1. Cocker bodies aren't really that light... any of them. WGP mechanicals and pumps are very old technology, back then weight wasn't something people complained about much. lol. I'd look at a 2k vert body (simple, plain, and looks solid). Or look at halfblocked bodies or midblocked bodies. The lightest pump body i've held was a halfblocked superbolt that had been midgeted.
2. As for AT, i may suggest reconsidering. AT isn't for everyone, and it can be a pain for those who don't know much about snipers. If your new to cockers, i'd say just go without AT for right now, until you believe it's required to compete. I personally dislike AT, only because it reminds me of playing semi-auto (style wise).
3. You could pick up a nice benchmark on ebay for $50ish with all the guts in place. CCM trigger frames are pure awesomeness. Comfy, balanced, and light weight. Although it isn't necessary, you would love a CCM frame. I shoot snipers with sliders and CCM Frames, and i have to say i don't have a preference right now. But check ebay for sure