First thing, call the Better Business Bureau or your equivalent and report the plumber. He should do better than that.
Second, the hot water. Go to your water heater and make sure the fill valve is open; some even put a valve on both sides of the water heater.
Third for the leak. With the valve open, use one wrench to hold the valve and back-up your turning on the nut the valve stem goes through (its called a packing nut). Usually you can turn it half a turn and eleminate the leak. It is possible the leak is up at the connection to the bottom of the tank. Stabilize the fill tower inside the tank and tighten the nut on the bottom of the tank with adjustable, groove-joint pliers (Channelocks), again half a turn should do the job.
Please let us know how it works out for you and we will be happy to tackle any other problems too.