TBH, I'd enable the exapansions just for the additional map types: concentric and clusters are two of my favorites. You can easily leave the additional minor factions and AI plots turned off, the increase in available unit types isn't going to overwhelm you (there's something like 100 in the base game alone, what's another 100? You can also selectively disable classes of units; e.g. teleporting, cloaking, etc. to simplify things, I believe there's also a dropdown that does something similar). You'll also have a wider variety of AI types to pick from, though I'd suggest individually picking from the Easier list and not turning on random types until you're ready (if you do, it's also a good idea to turn on 'reveal random AI types' if it isn't enabled by default).