How many actions can you take per turn?
Yes, from the turn overview of the game rules:


  You may build as long as your resource supply allows for it.


Also, the Combined Trade/Build Phase section of the Almanac states that


  After rolling for resource production, you can trade and build in any order. Naturally, you can trade, build, trade again and build again.


You are restricted to playing only one Development Card, however, and you cannot play a Development Card that you bought on your current turn.