Q21: Mostly has been answered, but you'll get this message periodically even when you're doing everything right re:establishing the colony. You'll often have situations where you'll see 2.56mil colonists where only 2.54mil can be supported by the infrastructure. In this case, unrest will rise by something negligible, like 0.04%, and can pretty much be ignored.
Note that you colony *will* demand protection once it reaches 10mil colonists and, should that not be provided for, efficiency will eventually reach 0%. You can also use a garrison force to quell the unrest, although you're probably more likely to do a combination of the two: Engineers to build the low end/nearly useless PDC to give the low amount of protection demanded.
Q22: Early on, I tend to avoid mass drivers for all but far reaching bodies (Titania, etc) that I'm no longer making regular deliveries to. They're an extra 300BP each, which is a significant amount early on. Only once I got my extra-solar mining colonies up and running did I start relying heavily on mass drivers in those systems (Actually, that'll be accurate in half a year once automine production resumes, still mass producing research labs).
The reason for this being that if you're still delivering the occasional automine to Titan, there's no reason your cargo ship can't take back the load of minerals with it.
However, should you have chronic shortages of minerals you're harvesting off Sol, mass drivers do make for a more reliable delivery method.
As far as getting the colony up, subsidizing the civilian sector is one excellent way to jump start their freighters/colony ships. Just note that they never upgrade their ships, so don't drop 50k in subsidies this early on.
Also, asteroid mining modules (only work on asteroids + comets) *only* drop minerals on the surface due to coding limitations in the game.
