hello Sypher
best place to start is the search - most topics have been dealt with at some point or other
for water that hurts you can make another brush over your water brush, give it a trigger texture and right click it on the plan view and set it as a trigger_hurt. Put dmg. as 150 and your water will kill
for your jpeg - make a new texture folder under the main > textures directory called whatever your map is called and put your texture in there. Make sure this new texture has dimensions that are multiples of 8 (i think) 32, 64, 128, 256, 512 etc.
2 sided patches im not too sure about but you can use invert matrix to change the side that is textured and also use thicken to give the patch another face.
keep at it 