My own surmisions and attempts to make sense of the manual, feedback welcome:
Planetary management
Quality
A planet's class determines the amount of usable tiles it has and the theoretical population maximium. Class 0 planets are completely uninhabitable.
Population grows by 0.2 b each turn by default, and other factors may increase or decrease this number. Planet quality doesn't seem to be among them, but a very small existing population does seem to have an effect.
Buildings and points
Each tile can support one project. The number of immediately usable tiles apparently equals the planet quality, but more (the non-green ones) may be made usable by applying terraforming technologies to them. Some tiles multiply the effects of a particular type of improvement if one's constructed there, and the more powerful multipliers may well tip the scales in deciding a planet's specialization.
Most projects are basic improvement buildings, which give small bonuses and can be built over and over, but others are limited to one per planet, race or game and more or less correspond to wonders in Civilization. There are only a few types of improvements, but several versions of each one. For example, the first factory will produce only 8 mp, but some way down the tech tree is one with a production capacity of 16 mp. Improvements can be upgraded to newer versions, and in fact are by default automatically added to the build queue.
Farms produce food, measured in megatonnes per week (mt/wk), which serves as the effective population cap. 1 mt/wk = 1 b people, up to the planet's theoretical maximium capacity.
Factories produce manufacturing points, or mp, which is the potential for shields and hammers - the stuff used to build military and social projects, respectively. More below. Research buildings generate technology points, tp, which are the same for flasks, the things that further research.
A great variety of factors affect influence points, ip, which give votes in the United Planets, affect the planet's loyalty and increase tourism income. Apparently the list can be viewed by hovering the cursor over the points. Ip are usable immediately, and needn't be converted unlike mp and tp. Specialized improvements can boost ip.
Approval, morale and happiness are synonymous, and the factors can be viewed by hovering the cursor over the percentage. Taxes and high populations are the big killers, improvements and high planet quality help. A 100% or higher approval doubles population growth, a 30% or lower one stops it and may cause the population to decrease. Low approval is bad news for loyalty, and the civilization's overall approval affects the elections in non-dicatorship governments.
Economic improvements are covered in the next section, but bear mentioning here for completeness. They simply increase the tax collected from the planet. There are also improvements that give military advantages, and every planet has a capital / initial colony that gives multipurpose bonuses. Improvements can be demolished immediately.
Economy
Taxes are a vital part of income, and the main purpose of citizens. They colonize planets and fight in ground assaults, but don't seem to have an effect on production (though I can't swear about very small populations). More citizens -> more cash. Economic buildings boost revenue, and there's the usual set of all kinds of possible bonuses. Note that higher populations do cause unhappiness. Tax levels are set empire-wide with a slider in the economics screen.
Buildings often have maintenance costs (which, with the exception of initial colonies, I've found to be trivial).
Construction
A planet can work on one social project (buildings on the squares and making them usable) and one military project (starships, given a stardock) at a time in addition to generating research. Unfortunately, the buildings generating the resources for this do nothing on their own and require funding to work. It costs 1 bc to generate 1 hammer, shield or flask (social, military, research respectively), so whereas in Civilization ten hammers only 'cost' the income that could've been generated had the city been amassing wealth, in GalCiv ten hammers means ten bc less for the treasury. A planet can focus on one of the three at the cost of the two others, but this is inefficient.
The amount of cash spent is determined empire-wide with a slider in the economics screen right below the tax rate. This slider is independent of the tax rate, and spending can well be larger than income. Similarily, spending on a planet can easily exceed its income. The three sliders below it distribute expenditure to the three kinds of production, but this is a bit I haven't been able to figure out - using 100% of industrial capacity doesn't seem to equal funding every factory and laboratory to their full capacities, as the sliders still affect things. Help?
Military production assigned to a planet is not expended if the planet has no such project, but instead is shown in parenthesis on the planet's screen and refunded. Contrary to the manual, this is NOT the case for social production!
