The two basic things I see are

TMI (too much information) - How to use the AI and ques.

Basic mechanics - How to move ships and use each screen.

A third thing could be to know your ideology and tech tree.

I think a lot of beginning FAQ's could be answered by having a very detailed tutorial options when starting the game such as follows...  Now from a developer standpoint this can become a very time consuming process but, may help players get those answers that they feel are too basic to ask but, can't figure out and get frustrated and leave the game.

Put in a tutorial menu into the game. (this would be different from the full tutorial already in place, just short 1-5 minute blocks that just answer these specific questions)

How to create custom faction?

• New game starts automatically
• highlights create custom faction and disables all other buttons, maybe even a text box popping up, even with voice over telling player what to do.
• Then walks the player through each step one by one with similar options all the way.

How to invade/capture another players planet/world?

• Game starts already in progress with a perfect opportunity to take over a planet within a few tiles of your shipyard/planet.
• Again start by having player select their shipyard and build a troop transport.
• Walk them through the process of sending ship to the other players planet and take it over.

How to construct a star base?

• One could create sub categories in this one for Economic/Military/Cultural/Resource/Mining.
• Once again game starts already in progress (preferably one which would be suitable for all of the above star bases, that way one could continue right into each option.)
• Have the player select their shipyard and build constructor.
• Walk them through selecting a good/perfect place for each star base type or even help the player choose by...
• Give them 3 or 4 options of tiles to build (with highlighting tiles) and ask them to choose which they feel would be a good location for star base, then if the player chooses poorly than maybe have a text and voice layover explaining to them why this may not be the best location for the star base.
• When they make a wise choice than once again open the text and voice layover explaining to them why this was a good choice.

Well I think this get's the general idea across, which one could expand on of course.  FAQ's are nice, however, most only give a basic idea of the answer but, don't always give the player everything they are looking for.  

Another option one could do is along with specific FAQ's answer the basic question and then include a link(s) either to the wiki relating to the specific question or related topics.  Also include in there quick links to other related FAQ's that may help answer other questions or where in the existing tutorial this can be found or if a more detailed based group of small tutorials are created than add which flow answers these questions.

Anyways those are my ideas on what may help newer players.

One could always expand on this for intermediate/experienced players to help fill gaps as well.