Most Source games found themselves CPU bound on resolutions of 2k and below. 1070 is a top-tier enthusiast card meant to drive recent AAA games, and is overkill (for Dota 2 only of course) no matter how one looks at it. As for RAM, it just takes however much you have for the most part. 24 GB isn't going to hurt in case of page pool etc. but I doubt you'll see any noticeable effect.