Every factions have certain advantages in their own culture. Those split into two categories: economy boosts and combat enhancements. The economy boost is the same for every faction, although the Advent can additionally boost this by using their starbase or researching special techs in the diplomacy research.The combat boosts are upnique for every faction, the TEC for example regenerate Antimatter faster in their own culture. The Advent gain more advantages in their own culture then the other factions do.

Also their culture is stronger than other culture. If one TEC culture center was on your planet and one Advent culture center was on the planet next to it the TEC culture would always be pushed back and your planet would gain negative allegiance rates. Of course this can change if the TEC player researches more culture upgrades than the Advent player does, but since the Advent culutre research has so many sub-steps it is unlikely to happen unless the Advent player is sleeping.

Yes, it is better to place the culture centers at the frontlines. However you should always have one or two of them in the back. If the enemy manages to destroy your frontal structures your culture will be removed from the map until you rebuild, taking away all it's boni and making you vulnerable.

If you want to push your culture into enemy territory in order to gain your own combat boni on their planet you might want to try building the culture center upgrade on your starbase. The culture spreading from there is as powerful as multiple regular culture centrs and it is also possible to spread it from neutral wells.

Depends: if both players are Advent they are pitted into a stalemate (that can be broken by placing a capship in your gravity well). If the other player is a TEC or Vasari the Advent culture wins under the conditions I mentioned. The Advent have one more stage of culture research than the TEC and Vasari have, and more additional researches now with Rebellion boosting culture even more.

Advent culture is NOT actually stronger, its more about having the upgrades sooner (and more of them).  One TEC or Vasari culture/media tower has the same strength as one Advent culture tower (ie: '20 Culture').  But opposing towers won't be a "tie" either, because culture repels much easier than it overtakes.  Culture leaving a planet is divided by the number of phase lanes leaving, whereas culture entering a planet has to overcome the full strength of the tower there.  In other words, culture is very easy to counter.  1 culture tower will usually counter 3 or more adjoining hostile towers!

For example:  if you have 4 planets in a straight line : A--B--C--D (and unupgraded culture), it will be a "tie" between 2 towers on B, against 1 tower on C; but visa versa the one tower on C is only sending out '10' against the '40' defending B.  1 tower on each would also be a stalemate, since they are both sending out "10", but defending with the full "20".  It would take 3 towers on B (=30), to overwhelm the 1 tower on C (=20). 

If the planets have lot of branching (phase lanes) rather than a straight line, it requires even more towers to overcome 1 defending tower.  (Note: Now you can 'tech up' culture output.  And Advent Starbases can put out "35" culture, with each upgrade).

At the start of the game, No!  But later, maybe yes.  Only one tower at your homeworld can eventually raise the allegiance of your entire empire.  Later, you might need to repel culture, secure uncolonized planets, or attempt a hostile take over from your border worlds.

Erm, I have trouble reading your post Won. To be more precise I'm not entirely sure which part of your quotes are quotes and which parts are cour comments on them. Care to cleanup that post so it becomes more readable?

Edit: Aha, thanks