1. I don't know.
2. No. You have to have a spaceport to get any resources/research/intel from a system (unless you have Natural Merchants).
2(a). A system computer only gives you more resources/research/intel if you are making them on a planet in the system. So, building one in a system with no resource/research/intel facilities does nothing. If you have no spaceport, the computer can't do anything, since you are making 0 resource/research/intel.
3. Yes. From Settings.txt in the Data subfolder:
Number Of Population Modifiers := 12
Pop Modifier 1 Population Amount := 99
Pop Modifier 1 Production Modifier Percent := 100
Pop Modifier 1 SY Rate Modifier Percent := 100
Pop Modifier 2 Population Amount := 499
Pop Modifier 2 Production Modifier Percent := 105
Pop Modifier 2 SY Rate Modifier Percent := 105
Pop Modifier 3 Population Amount := 999
Pop Modifier 3 Production Modifier Percent := 110
Pop Modifier 3 SY Rate Modifier Percent := 110
Pop Modifier 4 Population Amount := 1999
Pop Modifier 4 Production Modifier Percent := 120
Pop Modifier 4 SY Rate Modifier Percent := 120
Pop Modifier 5 Population Amount := 2999
Pop Modifier 5 Production Modifier Percent := 130
Pop Modifier 5 SY Rate Modifier Percent := 130
Pop Modifier 6 Population Amount := 3999
Pop Modifier 6 Production Modifier Percent := 140
Pop Modifier 6 SY Rate Modifier Percent := 140
Pop Modifier 7 Population Amount := 4999
Pop Modifier 7 Production Modifier Percent := 150
Pop Modifier 7 SY Rate Modifier Percent := 150
Pop Modifier 8 Population Amount := 5999
Pop Modifier 8 Production Modifier Percent := 160
Pop Modifier 8 SY Rate Modifier Percent := 160
Pop Modifier 9 Population Amount := 6999
Pop Modifier 9 Production Modifier Percent := 170
Pop Modifier 9 SY Rate Modifier Percent := 170
Pop Modifier 10 Population Amount := 7999
Pop Modifier 10 Production Modifier Percent := 180
Pop Modifier 10 SY Rate Modifier Percent := 180
Pop Modifier 11 Population Amount := 9999
Pop Modifier 11 Production Modifier Percent := 190
Pop Modifier 11 SY Rate Modifier Percent := 190
Pop Modifier 12 Population Amount := 2000000
Pop Modifier 12 Production Modifier Percent := 200
Pop Modifier 12 SY Rate Modifier Percent := 200
4. No, and they won't affect the ships of other empires that you have a Non-Aggression or higher treaty with either. They only affect those that you are at war with or have no treaty with.
5. The AI is mean and highly unpredicatble. It tends to not remember what happened even 1 turn ago. I suggest playing human opponents via
http://seiv.pbw.cc if at all possible.