I use both teflon tape and pipe dope. I put pipe dope on threads first, then wrap it with a little teflon tape. Just my preference. I feel it seals better so there is no leaking/dripping afterwards. Threads can be pesky sometimes, especially when you are mixing metals.
You don't have to, you can use either or, it's up to you. I use to use just teflon tape, which is fine 99 percent of the time, but I had to go back and fix a couple drips. That's when I started using pipe dope as well. I haven't had any leaks, drips or errors yet when working with threaded pipe.
Put on threaded side only - nothing on the union side that should be fine.
Let us know how it turned out for you, or if you need anymore guidance.