1. This is either if you want a simple planetary adjustment, for example, you play 1/49/50, and you have your CivCap already built out and set to produce one Hull per turn, and it lacks some MP to do so, set focus to it, so you reach what you want and don't have to adjust your whole empire.
It becomes globally important if your either playing on of the all-X strategies (only building either labs or facs) and use focus to get production in an area where you've not built any structures for.
2. Tech Inflation affects the research costs as you gradually research more and more. In TA it's really strong, with "red" techs heavy hit by it, sometimes weapons-costs will increase X8 by it. One reason to research "Planetary Invasion" very early.
3. Seems natural to me, but there is also an TA-only empire; the "Twilight Pub"
4. Ship defenses can be your friend, believe me, esp. in DA/TA. I've read lots of non-sense about it, it'S just that when folks are not able to use them properly they of course fail. Defenses give you a good edge very early on, even off-type defenses. Later on, when the Tech Inflation comes into play, it is *much more* easier to go up the defenses tree, as the weapons-tree. Especially because all AI's tend to research weapons and get stuck with it, and you can usually trade for these techs when your MMR isn't that high or you have an ally.
4b. This *was* right some years ago, under the old scoring system. There have been players who simply kept on playing and their games got bigger and bigger, leading to a 4mil pt game. After that, the games got re-counted by a new system which added another divisor by the turn-number, so that most of the old Million-point games got re-calculated to ~100k games.
5. Yup. Not counting Krynn and Korath.
7. If you are actually producing ships why not having mines? They do generate Influence (=Tourism income) as well. With the right level of Miniaturization un-armed Space Miners take no maint, produce a swarm of them and let them roam the galaxy; upon finish convert them to whatever you want, your investment is not lost. Playing around with asteroinds is meticulous, but it's actually a good way to built up new colonies, or force production on a planet that is near to a war or has a good StarshipQuality bonus. Or you let others do the work for you and flip enemy asteroids with a base, that can be done overtly fast.