Bases

On each base where you have a spacegate, click on the Base Overview page, then on the Options tab

There you can set if the spacegate will be public (available to other players), how much to charge for it in percentage, and the threshold (fleets under X size will not pay). You can also set who you dont want to use it.

There are astros that give you more economy or construction/production.

Crystallines are the best to economy; moon give 3 econ to your cristal processor structure, and planet give 4!

Metallic in the other hand give you more metal, so it make your base production and construction way faster. Moon give 4 metal and planet 5 metal. A metallic planet can easily reach production 600.

Check the Help about Terrains page to more details.

Starbases (SB) are similar to bases but on orbit.

You can have 1 starbase per base.

It gives you a estimative, what you will have after it is completed.

It is necessary to the system enable the queue links to the other structures that require the benefits of the previous one, like more power or population

If you have a few items on queue, and you add a Metal Refinery that increase your construction points, it may show a faster time than before to the previous queue items, it will be improved later

You need to build structures that generate Economy like Spaceports, Economy Centers and Capital.

Other structures also gives you economy; Urban Structures, Orbital Base, Shipyards, Orbital Shipyards, Orbital Base, Metal Refineries, Robotic Factories, Nanite Factories, Android Factories and Biosphere Modification.

One important point about Spaceports. The economy it brings is accumulative. Level 1 gives you 1 econ, level 2 more 2 econ, level 3 will result in 6 econ in total and so on.

Free accounts spaceports are limited to the amount of bases the player have. So if you have 5 bases, you cannot build spaceports level 6.
Premium accounts have no limits to build it, but the accumulative economy holds when the structure level reaches the player amount of bases.

Check this table: