Piping connections to water heater

I'll be replacing a gas water heater eventually and want to know the right way to install the piping to it. What I have now is copper male NPT sweat fittings threaded directly into the WH; cu tube is then sweated to the fittings at the WH. There is no dielectric union at the WH which I've read you should have for transitioning from steel to cu. It's been this way for 15 yrs and seems to be ok for whatever reason.

So, what is the right way to do this?

3/4 brass pipe nipple, say 4" lg; then a ball valve; then male NPT cu sweat fitting and then to tubing?

I am not in an earthquake area (east TN) so I don't think I would need the copper flex lines, but then again they probably wouldn't be a bad idea, and they do allow a lot of room for piping misalignment.

Many of the WH come with heat traps which also act as a dielectric union. If you didn't get corrosion on your old one, your water probably won't cause corrosion on the new one. See what the pros have to say. The addition of heat traps can save some money since they slow heat loss in the pipes when you are not using hot water. It's a good idea to insulate them as well.

There may be almost as many ways to connect that water heater as their are plumbers doing it. In any event, if you ask 10 plumbers how to do it, you may get 10 different answers depending on how they do it in their area.

amen hj;
almost all water heaters come with dielectric nipples already factory installed,
you "must" solder copper to fittings before installing on water heaters as they have
plastic inside that will melt if you use a torch on the top of heater

Flex copper is the preferred connector in my corner of the world. I makes the connection quite easy. We always use new flex even if the old looks OK. Some places require solid plumbing so you need to check your local code.

And those that do not use hard copper or copper flexes will use stainless steel flexes, etc.

..which are not to be confused with the stainless steel braided supply lines which (although they sell them for water heaters) are quite different. And I don't like them.