Anyone have an opinion on what NOT to do when developing a new game?

Yes, maintaining an active line of communication with your player base is essential. One thing I would emphasize is the importance of being open to releasing patches/balance changes in response to player feedback. Games being released in early access helps devs get feedback before a main release, and the backlash that can happen if certain issues aren't detected initially. If pursuing this route, or the game is releasing an expansion, it also helps to have a road map of planned changes and updates.