I think most of us know exactly how you feel. Do not over think it. Spend your time detaching and once you get that you wont have to worry about planning how you interact, it will be natural.
Answer important messages. By that I mean anything kid related, finance related, job/schedule related, etc. Ignore the ones that are pointless. Like if he sends you a text saying its hot outside. You do not care if he is hot outside or not, so you do not answer. Always be pleasant when you do respond. You want to convey your PMA and the idea that you are just fine without him. Do not worry about running into him with OW. If it happens it happens. remove yourself quickly, but as you say, with dignity. No point in having to endure seeing it if you do not feel you can handle it emotionally.
Me: 42 W: 32 Married 7 years together 8.5 S1: 7 S2:7 Bomb #1: 09-16-13 Recon #1: 11/13 A discovered 04-03-2014 W filed D 05-19-14 but never served me I filed D 12-02-2014 S 05-31-14 Divorced 5-19-16