I almost always have a starport on every planet. The initial colony structure provides a decent ammount of capacity by itself. An econ world with loses a stock exchange to make the starport, but you get to use the manufacturing capacity you otherwise wouldn't. You can't build big ships like this, but it's ideal for cranking out stripped-down constructors every few turns, or a decent transport every dozen turns or so.

Not to mention the possibility of needing an emergency ship exactly where you want it. Having a partially built ship in the queue makes buying that transport-stopper somewhat cheaper.

It's not a matter of IF but rather when... i don't build a StarPort on low PQs until much later or when my core network seems to be under scrutiny by a nearby opponent.

One rule of thumb to me goes like this; the further away from 'tactical' aims my ships can get, the more efficient reasons for starports. Knowing how fast any StarBases must be upgraded to be worth defending... a steady flow of Constructors is always welcomed.

And a rogue planet deeply inside a target enemy's territory MUST have one of those if only to defend it when & then without having to micman a full dispatch of support from other regions.

PQ1 or Twos are a different story; i'd use those as a spy base if EVER... but to make it dependant on flip tactics, there isn't that much room on these already to justify any development unless it can grow beyond PQ7+, fast. Including a slooooowww Starport output; well - maybe just for some cheap tiny scouts, though.

thx for the answers i always try to have a couple of core worls as my main manufacturing place and my border worlds just as temporary manufacteres.
When i play terrns i alweays construct starports but this seems to be changing now that im playing yor.

One more question.is it worht it to put a starport in a planet with no factories?

ive put some starports this way but even the costructors are dificult to make.

Is always dificult for me to decide wich planet wont be able to support a starport cause all my planets are avg i hardly make a especialize world.

Wich sends me to my next question, whats better? having a lot os especialize worlds or having lots of avg worlds.

Well, I build starports on every planets during my colony rush, since I colonize only initial PQ 11-12+ during this phase of the game, leaving those "crappy" initial PQ 10 and 10- for later on.

I have to say I'm used to play large or bigger maps only (difficulty now maso and usually slow or very slow tech, abundant all) since I like empire building and massive fleet battles. I do usually play my custom race, the "Teuffarz" with thalan tech tree and super hive and technologist party.

So those planets will be the backbone of my empire, thus needing starports. And during the colony rush, those planets will be producing small (then tiny) cheapest colony/constructors, then small "intrasystems defenders" (meaning those fighters don't have any engines, my usual fighters, any sized, got 2 engines.) when needed.

BUT when it comes specialization time, I sometimes upgrade the starport for a stock exchange or research coordination center or zero gravity entertainement, depending on uncommon planetary tiles wich makes worlds to be econ spec, r&d spec, all with at least 1 farm and 1 entertainement building (since farms aren't in Thalan tech tree I rely on alien tech trade to know how to build them). I usually build an eco starbase in every system with at least 2+ planets, it's a bit overkilling, and painfull to micromanage, but as I said, I like empire building
I usually build a real mobile military only when the colony rush is fully over, but it's another story

So for those backbone worlds, the construction queue at beginning is almost alway the same:

1)Recruiting Center (or industry)
2)Industry (or recruiting center)
3)Starport
3)Embassy (cultural victory alway off for me, but having a strong space is a key for a good empire)
4)Entertainement
5)Industry (or econ)
6)Econ (or industry or R&D)
7)R&D
8 and following) Depends of tactical and strategicals needs.

Edit:
Forgot to say that obviously, planets with initial PQ 7 and 7- wont be suited for starport, but sometimes terraforming could do miracles (giving you 3 more PQ per enhancement) giving you the opportunity to create a new manufacturing world, and strategical needs as said before (planets in the heart of alien territory) making starports (+ orbital fleet manager) a safespot for your ships or creating a strongpoint.

Needless to say, without any initial "racial bonus", a planet with a starport will need at least two industry buildings (later only one "industrial sector" if sticking to tiny cheapest constructors) to get a "decent" shipbuilding hability. By decent I mean 5-6 turns for those tiny constructors or tiny planet defenders. But nothing remplace a really truly shipbuilding specialized world (you know, 10-12+ factories, at least 1 powerplant, and with that wonderful Arcean building "Navigation Center" ).

Well it depend! ^^

If I know a world would need quick military build up, then yes factories would be front-loaded to insure quick growing of industrial capacity. But, during the colony rush, it is better to ease global econ growth by NOT building high maintenance buildings such as factories and labs.
Btw, don't overload social building queues, since when a new building is available, the upgrade come last in the queue, wich is in most cases, especially for factories, not good, adding much micromanagement to reorganize those already overloaded queues.

As far as I played, in every games, I alway run in deficit during the colony rush, taxes low to very low in order to keep a 100% approval rating for best pop growth bonus, global spending to 100%, mil spending set to 0%, and a smart balance between social and r&d spending. Usually around 40 social 60 r&d, updating it when necessary in order to insure quick tech discovery, and again, help ease econ growth since r&d without labs doesn't cost you much money.

My money income then mostly rely on tech trading (I really like those "minor civ's" since they are my "virtual wallet" ) and a little on cash giving anomalies (alway crossing fingers when scouting a new one, praying it won't be, as an assistant put it, a waste of time! ).

When the colony rush is about half on his way, I start light military spending to prepare for the ressource and starbases rush, assuming those starports are built or almost built.

I must admit you are right by not putting too early starport on planets to spare a couple bc who won't be used at this time, better place Starport in position 5) in my standard building queue during the initial rush. This queue is more an end colony rush phase, when military spending is already on, and global shape of different empires already draw, when you grab those harsh conditions planets.

I have to say again, it is a bigger map strategy, I know it is a bit different on smaller maps.