[akots]

7. Depends on particular situation, there is no universal recipe. Some AIs (Tokugawa etc.) will trade only later in game and only with a very nice relationship. Most AIs do not trade most valuable techs until much later. Diplomacy is more tricky and less clear since there is a lot of hidden stuff.

8. If you are big, they can be used to pay maintenance for the empire. Some cottages are always useful and cottage spam is a good way to win space race or get early cultural victory or stay at parity with AIs on higher difficulty. Early in the game especially with financial trait they would keep you afloat while you expand. If terrain permits, building a few in the capital is a good idea because they are multiplied with Bureaucracy (unlike specialists which are not multiplied). There are also a number of things written about city specialization and micromanagement of specialized cities. Cottages in research centers is a very good idea. Improvements there (Granary, Library, University, etc) are usually built with chopping or pop- or cash-rushing or by switching to high-hammer tiles while sharing cottages with adjacent cities. Just keep in mind that to grow, cottages have to be worked all the time.

But this game is very complex, there are many things written already and even more things missing. What I'm saying here is all IMHO and a few very general statements not applicable to every situation but to many situations. They help to survive and get familiar with the game at the beginning IMHO.