The question you need to ask yourself is "Is it worth it?". I don't want to add to the 5D3 vs 6D friction, but there are benefits to each. Want to upload directly to FaceBook? The 6D has built in wifi. Want to shoot 6 fps? The 6D can't. Need super fast AF outside of the center point? The 6D may not be your camera. Shooting a lot indoors without flash in very low light? The 6D might be better both in terms of focus and very high ISO performance. Do you plan to shoot video? The 6D has fair to poor video performance. Look at the pros and cons (there are others) and decide if it's worth the price difference. Also, take into account whether you can live with the "less capable" camera when you could have had a "better" one. Some people can't. There are some analyses at http://www.kenrockwell.com/canon/6d/vs-5d-mark-iii.htm
I agree with the "get the kit now and see how it goes" folks. You'll have 24-400mm covered. Then you can see what you have and what you use. You can sell the kit lens for a profit, as has been said, and buy the Tamron 24-70 later.
If you want a good bargain in a portrait lens, add an 85/1.8. It's superb, especially with the built in corrections of either of the cameras that you want.
Just remember that, while you don't do much flash photography, fill flash is important for candids that are backlit. It's much easier to get the shot right than to try to fix it in post. Neither of these cameras have a built in flash. I picked up a used 220EX in like new condition on eBay for very little. It also has the advantage of AF assist, although with the 6D you'd hardly need it. I don't use it for exposure, just for fill.
Another consideration is to sell the 50/1.4 and get a 40/2.8 pancake. It's a wonderfully light lens, and easy to carry around all day. The images are great, and the wider angle is closer to "normal" than that of a 50mm. The 50/1.4 is great for low light, but again, these cameras, and especially the 6D, do well in low light.
The thing to remember is the three things that make an image are, in order, the photographer, the lens, the camera. That's my opinion of course, and you know what they say about opinions. You can buy a very nice lens for the price difference.