In Takenoko does the player have to choose both their actions before performing either
The actions are chosen and resolved sequentially as you have been playing, so you can see the result of your first action before choosing and resolving your second action.

While the original rules do seem to indicate that your two actions must be chosen before you resolve anything, it was clarified in the official FAQ:


  The two actions are chosen sequentially. This means that if a player choses to draw a new objective card, he can look at it before deciding what his second action will be.


Note that most of the official links to the FAQ now seem to be dead, so I assume that since the FAQ was released in 2012 these changes may be included in newer editions of the game.