To select multiple objects you can hold 'Ctrl' key while selecting objects or click and drag on the terrain around them.
You can "mouselook" by pressing and holding the middle mouse button in the display window.
You can add multiple objects of the same resource by holding down the 'Shift' key while you place them.
You can set the height and the speed of the camera in the tools menu.
You can move the camera laterally by holding down the 'Alt' key and pressing either the left or right arrow keys.
You can rotate the camera up or down by holding down the 'Alt' key and pressing either the up or down arrow keys.
You can move the camera vertically by holding down the 'Ctrl' key while pressing either the up or down arrow keys.
You can move the camera's position by clicking on the Overview Window.  You can also drag the camera around the terrain in the Oviewview Window.
You can change the camera's rotation by right clicking in the Overview Window.
Use the Translation Window to place and orient an object precisely.  You can open this window by right clicking on the obect in the Display Window or the object's name in the Instance Window and selecting the Translation menu item.
There is a backup option under the File menu item that will backup your previous data every time you save.
There is an autosave option under the File menu item that will automatically save your mission at a specified time interval.
If you want to delete a mission, it is best to do so through MUGE rather than Windows Explorer.