To make the crates stay in one position, select the crate you want (in Valve Hammer Editor). Right click on it (on the grid) and choose "Move To World". This will make the crate only a brush, and not a entity.
To make doors open with the push of a button, follow these steps. I wrote these steps as if you already know how to make a door.
1. Make the door like you normally would except one change.
2. The change is, add a name to the door, such as "door1". Something easily remembered is nice.
3. Make another brush that you deem to be your button.
4. CTRL+T (Shortcut to make a brush an entity). From the drop down list choose "func_button".
5. First things first, go to the "Flags" tab, and choose "Don't Move".
6. Next click the "General" tab. On this tab put the name of the door in the TARGET field of the button.
7. Mess with other values, such as speed which is how fast does the button reset I believe.
To make ladders.
1. Choose the texture you want for the ladder, and make your ladder brush, and put it where you want it.
2. Duplicate the ladder brush and put it right in front of the your other ladder brush.
3. Click the ladder brush that is in the back, and press CTRL+T.
4. From here, choose func_wall from the drop-down menu.
5. Now select your other ladder brush, and press CTRL+T.
6. From this box, choose func_ladder from the drop-down menu.
7. Voila.
