newby questions

AS I recall, there are two lines of research for Starbases. One for weapons and one for defense, just like for ships. After researching each level, you can add a module to the SB for defense or weapons. You really need to do both. In the end game, the maximum defense of a SB is insufficient to keep it alive against the top weapons.

Try adding the first starbase weapons tech (laser+1,missle+1,Gun+1). After that the next consructor you add will allow for either armour+5, PD+5 or Shield+5. So after adding 4 constructors to the basic starbase it should be +1 in all weapons and +5 in the three defense techs.
Good Luck and have fun !!!

You need the Starbase Fortifications techs to add the modules needed for attack and defense of the starbase itself. The Starbase Defenses path allows starbase modules that assist ships attack and defense. There are also a few random weapons techs that enable miscellaneous modules from both branches. I've never used the Starbase Fortifications path, I don't think it's really effective. I just dedicate a fleet for the starbases's protection.

The battle station series that adds all weapons and all defenses (to the SB itself) are enabled by Space Weapons then Medium, Large and Massive Scale Building.

I will try this, even if according to manual there should be no need of upgrading the weapons to +1,+1,+1 as prerequisite for installing defence modules. If it's really as you say, then starbases are doomed in my actual game (there is a council law into force that block players to add more than 4 modules per starbase).

Thanks aniway

4 modules? no real problem.
Put 'Battle Stations 1' on to keep simple attack craft at bay, then put 3 mining modules on to get the bonuses.

You wont ever stop a fleet since no matter how many weapons you put on a starbase it can only shoot once per round in combat so it can only ever kill 1 ship at a time at best. By putting one Battle Stations you stop cheesy outdated ships wiping out your SBs if you are at war. Or you could get 4 mining modules and just 'suck it and see' how long it lasts all alone in space...

Think of it this way: defenses won't do you any good without weapons to fire back! Otherwise, it's simply a matter of time before the enemy penetrates your defenses with a lucky shot.

Researching the ship defense technologies also yields starbase defenses, though only in the highest tiers (Overlord Armour, Electromagnetic Surge, Invulnerability Field), each giving +16 in their area of expertise.

Also, keep in mind what Mumblefratz mentioned: Starbase Defenses is for military starbases to assist ships in the zone of control, while Starbase Fortification is for the personal defense of starbases.

Don't forget you can leave the UP if they nail you on starbase modules (they did so with me, and I quit them). Think of what is more important: trade routes or your starbases. People will not automatically go at war with you because you've left the UP, but they may start to dislike you for not trading with them.

I never bother wasting constructors on weapons and defense techs. I just max my mines extraction capabilities. Max econ bases econ and trade bonuses. The same follows for influence bases.

I find the constructor stage incredibly boring and want it over with as soon as possible. Starbases are no match for max'd out fleet in a war anyway so building them up for other then their primary purpose is a waist of time. I can park a fleet on them if it is that important to me.

Rarely do I see the enemy worrying about attacking my bases even located in their territory when I’m taking 4 or 5 of their planets every turn.

Good points.
For now I will forget defences and add 3 mining modules and 1 level 3 weapon (I've already have the tech and attack 30 should keep at bay every enemy fleet at the moment). for bases more exposed, I will add a fleet.
Leave UP? No thanks; trade represent a large part of my income.