They shouldn't generate until the extractors are completed. You're not playing with quickstart where the extractors are already built are you (quickstart was of course added in Entrenchment)?

I can't seem to replicate the problem: although the infocard for the planet will always show the extraction rate for when the asteroid is finished, the infocard for the asteroid (mouse over it directly) will show 0.00/s until it is built. Similarly, I don't see increased income until the extractor is finished. You should be aware that capital planets always generate 4.0/s tax, 0.4/s metal and 0.4/s crystal (at normal speed and 100% allegiance) by default, whether they have any population or resource asteroids; perhaps this is what you are seeing.

It's the home planet bonuses for tax income and extractors.

You'll need to edit every Planet[Name].entity file and set the path:Home to NOT give a metal or crystal bonus.

You'll need to edit the GalaxyScenarioDef for the normal start option for each faction.

You'll need to edit each map (*.galaxy) you play and set the normalStartHomePlanetUpgradeLevel's to whatever you desire.

This is done the same way you would remove a factory. Also, additional constructors are added by purchasing logistics or tactical slots. You would add back in the additional constructor by editing these sections of the Planet entities.

Thanks for the info ZombiesRus5. I can create it as a mod, can't I.

There is... 

The easiest way is to download the reference files from Harpo9999's link.

You should be aware that changing anything about homeplanets have serious effects on the AI. Like Lavo said. Basically it can make them sitting ducks, and you will have tremendous advantage from knowing what to do but the AI doesn't really.

copy the galaxy.manifest to your mod and add you new map to the list. 

Be sure to increment the count for each map you add.

Ok, I was doing it the hard way - good learning curve though. I redid the whole thing.

What I've done now is created a mod that changes "quick start" to "slow start". When you choose your game options you can choose between those two - quick start is gone! Also, I copied and changed every map, not that I know if every map will be appropriate but they're all there. I noticed that some maps have their own override for starting ships etc in which case, the slow start will not be fully effective.

The MOD works this way:

Normal Start - As per the standard game except you only get one frigate factory instead of two - the way the game use to be in previous incarnations.

Slow Start - It is as if you have just colonised the planet, there are no planetary enchancements. You have yet to even establish your Empire's capital. You begin with one constructor only.

Now, where can I upload it?