The liver is a really great idea, actually. I'm not terribly fond of it, so I don't really think of it. But livers are cheap, nutritious, and easy to come by. I see no reason why a paleo-type diet wouldn't be okay. Honestly, that's what babies really need as first foods, right? Good proteins, fruits, veggies, and unprocessed oils... Sounds like great things for babies.
I have let DD have a few bites of my oatmeal, and some brown rice cereal (I ground the rice and cooked it on the stovetop), but that's probably about the full gamut of grain she will get until at least a few months down the road. I've given DD some ground beef, and also a few bites of chicken, but she seemed none too pleased about those.
In many cultures, meat is the first food. I wouldn't think you'd have any issues with a paleo focus for first foods.