Yes you should deadhead. A sunflower is no different than any other flower. A flower's main mission is to set seeds. Once that's done it shuts down flower production.

No it is not necessary to pinch them back.

I would not pinch. Once the main stem starts to form a bud it will naturally start sending side buds.

I would deadhead them, it will send up more flowers and it will help keep the weight of the stems down.

Both of these have a beautiful shape without pinching, and will send ~50 flowers out naturally : )

Keriann~

Thanks, Oilpainter and Keriann, that is very helpful information. I had no idea each one would make so many blooms. I am glad you knew about those varieties Keriann. I picked them because they are smaller than the giant type. Will post photos when they bloom.

One reason not to deadhead is if you want to leave the seeds for the birds (as I do).

I hadn't heard of "Incredible." I'll have to look for it.

Incredible is supposed to be a dwarf type. But the seedlings are larger than the Teddy Bear seedlings. I am excited, they are doing great. I will leave some for birds and deadhead others. They will be mostly in containers so I hope they do well, the package said they were good for containers.
Susan.