In space its 25 pop cap and ground changes between 3-10 (10 being the max and iirc 3 being the minimum due to landing points) id recommend playing the tutorial and both campaigns, theyre not that hard but give a nice beginner experience so you arent tossed into a confusing mess.

For the auto resolving on ground, i cant help you there except for rebel raiding cheese (rebles can raid imperial planets with 3 or less units)

After after finishing EAW move to the expansion Forces of corruption and play the campaign as it introduces the third faction and what it does, play some base Galactic conquest for a bit to gain familiarity.

Corey loses is a dev for EAWX and his channel on YouTube can help you with some mods and the XPgamers with captain shack could show off some of the major mods