Your going to get a wide range of answers, because aurora is just one of those games with no right way to play - even getting pasted by the first npr you encounter isn't a loss really - empires fall, its just that in aurora it can be yours too.
I can weigh in on the first two at least.
1) I always have more and more labs in construction. I only stop making labs because I have a resource shortage, a population shortage, or an income shortage. I have a low tech rate game(10%), where I had a absolutely obscene pile of mercassium on venus and mercury, so I've built a ridiculous number of mines, automines, and labs(620 labs on earth) and I occasionally bump that further as population allows. When I finally felt brave enough to leave sol, since I'd done a conventional start, I found that I was quite far ahead of the first npr I encountered.
2) Military buildup, at least enough to defend myself, starts as soon as I start leaving my home system. Before that the chance of an encounter is very small, so I push techs, and keep some small craft designs ready so I crash build a missile based defence if I need it. Usually around Ion I start launching offensives, though in the game I mention above, that started with Nuclear Pulse engines, since I had a few resource shortages to resolve, so I had to expand quickly and find them, and expanding means encounters in the near future.
3) I don't use them either, so I'll defer to those who do for reasons why you want to.
4) is possibly a bug report.
5) is I think something you cannot do directly, I don't recall aurora ever letting you do that. That said, you could create a colony somewhere you don't car about, say, a random asteroid, ship them there, and abandon the colony. You don't get anything back, but they are effectively "decomissioned"