You can get 4 on neutral gravity wells (gas giants, asteroid belts, space junk, plasma storms)

There are two reasons to build more media hubs.  First, culture spreads faster, and second you can drive off competing enemy culture more easily.  If there is no competing culture, the only benefit to multiple culture centers is how fast it spreads.

Usually trade ports.  If it shortens your maximum trade route, you may have to make a decision.  If you decide not to put trade ports on the planet, and the loyalty or resource levels are too low to build refineries, there may not be any use for those logistical slots.  However, sometimes having 4 or 5 factories on one planet can really help churn out units if you get in a fix and need rapid reinforcements.

Leaving those logistical slots empty isn't necessarily a bad choice.  It costs you nothing and you still get all the other benefits of the planet.

Cheers guys, very helpful.

I'm now wondering if it's possible to ALT-GROUP up shipyards across severals planets and have them all build units and send to a specific location. make for some nasty reinforcements when coupled with phase gates.

on newplayer's response:

Although the games AI may choose a path to give you the best benefit it will still only pick this from a list of shortest paths. I try to force it it following a snake path around my systems with a trail of trade hubs. The real question is am i making money by leaving some systems bare?

Just click on the planet and select the "create frigate" button from there.  It will automatically split the work between your frigate factories.

As Hack mentions, you do need to hand-craft your longest trade route.

Picking what to build where can really depend. I play TEC mostly, and when I run into desert world my usual inclination is either to turn them into an econ giant or a forge world with as many shipyards as i can cram into it. Of course, it varies based on your situation and map. If there's only one desert planet but it's at a great spot for attacking or defending, you might want lots of shipyards. If it's farther back, trade ports are probably better. I suppose you could put a ton of research stuff into it, but generally i'd think it would be better to spread those out to prevent a single attack from knocking you back to the stone age, so to speak.

Culture is another option, one which the ai occasionally seems to like. It's annoying, but since culture weakens as it passes thru each gravity well and divides itself up across phase lanes, your money is probably better spent dividing up the culture generators and going with one of the others, unless you're in a culture war for some reason. That said, I played a game against the ai where it pulled an all-culture desert world on me, and between that and having a half a dozen broadcast centers spread out across adjacent jumps, i ended up losing several gravity wells and almost losing a few more before i built enough of my own to counter them. As such, in some situations it's possible for culture to be a good choice, assuming the planet is well located and you get the element of surprise. Just make sure to capitalize on the situation before a) they build a bunch of their own culture centers or they send a huge fleet to pull an Alderon on you... unless, of course, that's what you want them to do.

Overall though, culture is too slow to make much of a difference compared to either of the other two main options (loads of money or mass production - i imagine the vasari could do really well with a single centralized shipyard and some phase gates). The bonuses it gives are nice, but not earth shattering. Im not sure off the top of my head about the Advent or Vasari, but the TEC just get extra antimatter regen IIRC. As such, 9 time out of 10, extra logistics are best spent on a well planned trade route, particularly if you can route it through a desert world. Just make sure when you start building to have a clear idea of what your current territory is, your likely future territory will probably be, and plan ahead. Put research stations away from your best possible trade route where possible, if you're the TEC remember you can research to get an extra 4 spots at EVERY colonizable gravity well (even the dead asteroids), and if the game is likely to go on long enough, make sure to plan for the possibility of enemy culture on border worlds.

Again, thanks for the thoughtful replies, guys.

Do suns/wormholes allow trade routes to pass through them in Entrenchment as well? Or have they removed that since it's possible to build a conducting starbase on them? I have a lot of testing to do when I get home from work! I'm also keen to hear what some of the longest trade routes have been.

Again mentioning the using the ALT+# groups for shipyards, I don't recall if you can hotkey structures, let alone across several planets. But this would be great for pumping out huge quantities of ships fast.

Ah well. Nudge nudge devs. heh

Probably worth filling an entire desert planet with shipyards then rather than splitting them up

The most extreme example I've seen, is each trade port earning 4.4 inc/sec.  That illustrated example also includes a good explanation (and illustration) of the negative result of 'spamming' tradeports.

On the small Derelict map, there are a couple ways to make an 8 chain route with just 2 tradeports!

It also easy to make very long trade routes on the small Agamemnon's Bounty map with few planets, and that might be what the map description: "only the most cunning grasp the greatest rewards" is referring to.

Mind you, these are using vanilla Sins.  As mentioned above, Entrenchment traderoutes DON'T automatically extend thru uncolonizeable grav wells like the original Sins did.

Regarding culture, only ONE media center can eventually accomplish the same increase in allegiance/income as many. 

Trade ports are usually your best use of extra logistical slots.  But sometimes, building enough [8] civil labs to get the 'super techs', like Pervasive Economy or RA can be a better payoff.  Finally, lots of military labs [8] are required for the super weapons.