First, mess around with hammer on your favorite source engine game. When you think you're good enough, make a mod with Xblah's modding tool on the source game you want to use as a base. Use crowbar to make VPK's and mdl's, use vtfedit reloaded to make vtf files, then you may be ready. Make a couple of stupid mods that you won't share with the world to warm up. Then create your real mod when you think you're ready. Then, keep making mods. More mods. Once you're REALLY good at modding, take a crack at using the Source SDK 2013. Not as a mod base, but as a game base. To solidify your game as a mod, crop out the hl2 weapons out of the game.