1. I buy a lot of tiles early. Sometimes even if i don`t need them immediatly just to get them while they are cheap. Unit upgrades are the other big part of my expenses. I usually don`t buy buildings/units, only to get heurekas in time if needed. 2. That really depends on the game. Basically you want to finish the tech tree, Big Ben and Democracy as close as possible. A rough benchmark for a game that lasts about 160-170 turns is 35k gold for all the great scientists. You need to get a feeling how long it takes to save around 17k gold. In my experience gold is never the problem. Production time of the spaceport and finishing the tech tree are the bottlenecks. 3. Only the very last cities don`t get monuments. Most conquered cities do have them, if a conquered city doesn`t have a monument i usually don`t build it and focus on districts instead.