Technically, you can play multi player with yourself. You can't be alone on the map though. You can play just about any multi player map this way, just make sure not to accidentally win (or lose).
And there are no bots, there are only level-specific AI's as of yet. The construction of a Generic AI has taken many forms, few of which have had any results.
I myself planned on working on such a generic AI, but it will take at least another 10 years before I get through with it. Complex game, lots of rules and situation, not easy.
Playing multi is a good way to gain some skill. But then you just need a lot of practice to learn the tech trees well enough.