Some good points there thresher.
Agree what you all want out of the game and the group within it. A social node, a military powerhouse, a political cabal, or what.
A little bit of out-of-character social contract. One of the simplest declarations with my first Empire group was “everyone is IC loyal to the group, at character generation”, meaning that we started with no internal PvP, but with the possibility of the game and events driving a character into treason.
You will also want to agree on contributions to group stuff. Who’s getting the tents, the food, the beer? Who’s doing most of the set-up? Who’s running things OOC? An efficient way to destroy a group is to leave one guy handling the financial and labour costs for a group, feeling taken for granted, and leaving with the group tent and set dressing…
Work out what contributions can be made. Costumes, set dressing, tents, food, drinks, props, time, cash, washing up… everybody needs to pitch in to some extent. Even if all you can do is be around to help unpack and packup the group tent and camp, that could be a godsend.
In game contributions. Check that everyone is keen about what they’re doing on the field. “We need an X, you can play our X…” is a likely way to get your group X to never come back.
And for planning a new group in Empire, which has some lush costumes and wonderful immersion… sort out the colour scheme and/or group imagery as soon as possible, as a group. Plenty of advance notice is needed to make individual costumes with a unified look.