I meant to reply earlier, but the afternoon got away from me and I only just sat down.
I would keep the plan simple and not overthink it, especially if everyone already sounds open to something low key.
I usually start by picking a time first, because once that is settled people stop suggesting ten different options.
If the weather looks iffy, I always bring an extra layer and a small notebook just in case we end up waiting somewhere.
I also like to send a short recap after we decide, because otherwise I forget the small details myself.
Honestly, that saves me more than anything else.
If you want, I can help tighten the wording before you send it so it sounds friendly without being too wordy.
I think you are closer to having it figured out than it probably feels right now.

I finally had a minute to think about your question, and I would probably handle it in the most ordinary way possible.
If people are already loosely agreed, I would send one clear message with two simple choices and then leave it alone for a bit.
That usually gives everyone room to answer without turning it into a whole side discussion.
I also noticed that when I stop trying to perfect every sentence, the reply sounds more natural and people respond faster.
If timing gets awkward, I would suggest moving only one part instead of reworking the whole thing.
That keeps the energy calm.
I can also read over the note if you want another pair of eyes.
I am around later this evening, and I do not mind helping trim it down so it feels easy and direct without sounding abrupt.