Can I extend my stay after 180 days on a DTV visa in Thailand?

In theory, yes. Benjamin Hart from Integrity Legal claims you can't, but unless he has some sort of inside information we don't have, then he's speculating.

What we've been told so far is that yes, you can extend once per entry for 6 months.

In practice, unless you are infirm or can't travel, you're better off traveling and doing a border run or having a vacation/holiday at least once every 6 months and then returning. Seems to be easier that way but up to you.

Yes. 1st time at Immigration.

Yes, and at the end of the extension you will be required to leave the country (even if only for a few hours) and get a new 180 day entry stamp when you return

According to the rules you can. Did your research tell you something else ?

You can but as yet no one knows the requirements that will be needed to do so.