The crates should just be func_breakable. I would think the prefabs would be like that already... no?
To make your own textures you need to make .WAD files. You can make .WAD files with a program called Wally:
http://www.superjer.com/files/wally_155b.exe
IMPORTANT!
All your textures should be 256-color and one of these sizes ONLY:
32x32
64x64
128x128
256x256