It is made of aluminum. It will bend easier than steel but won’t rust.
The opening in the fitting measures 1.3 inches. That matches up with the OD of 1-inch PVC pipe.
Depends on diameter of heater, pan should be a least 2 " larger than tank
Not much clearance, if tank is full too heavy to lift.
Metal hose of coarse.
The pan comes with a pvc fitting which fits into the side drain hole and can be easily plugged by a male threaded pvc plug if not connected to a drainage pipe (not recommended).
You can place a cap on threaded connector.
If you don't have a drain pan, you should get one. Because, it will catch any overflow caused by a leaking connection or the pressure relief valve, the heater drain, etc. etc.. Do a thorough inspection to determine the leak source. It could be a simple fix. Unless you take it apart after you've installed a new heater you won't find out where the leak was until afterwards. And sadly, it's too late. Your chances of bragging about your 20 yr water heater just went up the basement stairs. Unless you have no problem throwing down a payment, don't immediately blame the water heater. A wise old mechanic once said, "I've aligned more front ends, with a grease gun than with a wrench....
I would suggest talking to a plumber, I don't think it would be as easy as one in the garage.