three n00b questions: what criteria should I use to decide if I should build a farm or a cottage? the AI sometimes highlites both, and so I have no idea what to pick, I am sure that there must be reasons why I would pick one over the other but I have no idea what those are.
Farms give food, cottages give commerce.
If the city is too low on food to grow, a farm is better.
If the city is a dedicated Great Person Farm or simply designed for assigning specialists, a farm is better.
If the city is specialized in production, a farm is better.
In all other circumstances (= the city has enough food already, is commerce or hybrid, you don't run a Specialist Economy), a cottage is better.
Note that if the city has enoug hfood already and is dedicated to production, a watermill or a workshop can be even better.
second question: I've got a city that is unhappy. I've built all the happiness improvements that I have the research for, what else can I do to improve the happiness?
check my signature for a complete overview (edit : right word at the right place) of happiness
The most efficient way to get happiness is to expand your land and grab loads of happiness resources + building the things that give the most happiness bonus for the resources you have.
For example, if you have gold, gems and silver, you should rush to Metal Casting and build forges.
HR of course is a definitive answer to happiness issues, but it's rather costly IMHO.
third: it seems really hard to take enemy cities... I build about 10 catapaults, push them over to the cities, bombard until the city defenses are 0% and then try to attack, but I loose pretty much all units (catapaults, swordsmen, etc.), what am I missing?
promotions, maybe?
Or just numbers?
If you attack superior defender (= less than 50% odds when you attack), you should have superior numbers (= at least 2 units per defender).
If you face overwhelmingly superior troops (=less than 10% odds), you should have overwhelmingly superior numbers, including loads of catapults that you send in first.
Don't let the enemy heal between attacks, all your troops should attack in the same turn.