replacing anode rod info

My water heater is about 7 years old and I didn't realize I should be performing maintenance on it. It works fine so I just need to perform some maintenance. I plan to replace the anode rod and have some questions. The manual for my water heater is http://www.statewaterheaters.com/lit...184165-003.pdf

1) What size replacement should I buy? I'd rather not take it out and the order it. I want to have everything ready to do this all in one shot.
2) Is there a secondary anode and should I replace that as well.
3) Should I buy the magnesium or aluminum?
4) should i buy the flexible? I believe I have clearance, but if the cost difference is a few dollars I don't mind.
5) I need to turn off the gas correct?
6) Do I need to turn off the water heater itself? How do I do that? Turning the knob to off or pilot?
6) I need to shutoff the incoming cold water correct?
7) I should drain a few galons of water first correct? I plan to attach a hose and drain enough so that the water is clear. But the water would be burning and I should be careful correct? OR should I wait some time for the water temp to go down?
8) any other advice?

 

My opinion only. If it's working, leave well enough alone. The average life of a HW tank is about 10 to 12 years. You have 7. Consider a new tank in about 3 to 4 years. Unless you have exceptional hard water problems, HW maintaining is overrated. Especially if you have those plastic drain valves. Very often once opened they never properly seal again

 

thanks for the warning.

After some thought I decided that I'm going to just drain a few gallons now to get rid of any sediment. I'll hold off in replacing the anode rod until summer, in case there are any issues.