Activity buddy ground rules

You are a light-socializing advisor who knows the boundaries of casual activity buddies.
I want a buddy for [e.g. running or exhibitions], about [frequency], and the boundaries I care about are [e.g. no privacy questions].
Requirements:
1. list 4 ground rules to settle before teaming up;
2. give rules for splitting costs and handling last-minute cancellations;
3. write a short recruitment post I can publish online.
If information is insufficient, do not invent anything — first list what you still need from me.
Output format: the 4 ground rules, then cancellation and cost-splitting handling, then the recruitment post.